I just had a look at the photos in the link you or the other gentleman supplied and suspect that we may end up comparing three different things here the Blenheim IV, the Bolingbroke IVT, and the Pima static display using a Bolingbroke IVT with additions to make it look like a Blenheim. Please understand that I'm not trashing the job they did... more an explanation of detail differences than anything else.
I'll attempt to tackle your points in the order in which you presented them, and throw in a few more bits and bobs.
The extra bulbous starboard nacelle fairing was a feature that differentiated the Bolingbroke IV (and derivative IVT and IVTT subtypes) from the Bolingbroke I which was, in turn similar to the Blenheim IV in this area. Basically it was one of the results of a revised oil system, designed after operational evaluation of that on Mk.I aircraft determined that a system more suited to the range and climate environment typical of Bolingbroke (a maritime aircraft as first employed by the wartime RCAF) operations.
The port nacelle upper fairing does not feature this bulge, though it may be more "humped" than that on UK-produced Blenheims. The port nacelle fairing on the Bolingbroke IV is longer than it is on the Blenheim IV or Bolingbroke I. It was redesigned at Fairchild Canada to accomodate a larger, faster-deploying dinghy than the "valise type" dinghy stowed in the cabin of the Blenheim IV and, IIRC, the first Bolingbroke I's. This dinghy has external (handle recessed into the port wing fillet trailing edge to fuselage joint) and fore/aft cabin internal manual Bowden cable releases, as well as an immersion / impact switch release circuit. Though I don't recall seeing it in the documentation, I believe that another reason for the external stowage was the rear cabin being redesigned to accommodate two of the Bolingbroke's four man crew vice the three-place Blenheim's single rear cabin occupant. The maritime GR mission also increased the volume of radio gear carried back there.
The odd scalloping in the forward cell of the port-side nose glazing appears to be an artifact of this particular restoration and not present on operational aircraft. I'm pretty sure this area was identical on the Blenheim IV and Bolingbrokes of all marques.
Engine cowls were the same for the most part as I recall (though, while I think of it, the maintenance latches may have been different), but there were detail differences adjacent to it. For example, as part of the extensively revised heating system, Bolingbrokes had intensifier pipe intakes ahead of the exhaust outlet pipe take-offs where the Blenheims did not. Later production Bolingbrokes had additional bell-shaped intakes (4 IIRC) added to the inside of the upper lip of the exhaust ring. This appears to be a feature of the power eggs used in the Pima restoration. It came to the Fairchild line very late (perhaps only on T and TT aircraft).
With the revised heated carbs came new Fairchild designed intakes below the cowls simple sheet metal shapes vice the streamlined ones on the UK produced aircraft.
Not so sure about mainwheel differences. I can look but memory tells me the specs were the same.
The Bolingbroke main gear structures were almost identical to the modified Bristol gear that went into production in late 1939 on Blenheim IVs (sorry, not sure when) where the Blenheim Is had a more simplified gear. I say "almost" identical because the Bolingbroke had several additional safety features to prevent "kneeling" at higher operational weights. From a scale modelling (modeling? maudlin?) point of view they're hardly noticeable, comprising a locking plunger and a slight over-extension of the radius arms at their folding knuckles. Not sure how these would show in a comparison though. I'll have to have a look at pics and manuals later on to discover if these show up physically and get back to you on it.
There were minor changes in glazing and associated framing over the evolution of the type. Especially around and above the pilot. With the possible exception of an additional crossbar on the sliding roof panel over the pilot's cockpit, I believe the Pima a/c, based on a Bolingbroke IVT as it is, is similar to non-maritime Blenheims with flat side panels. Maritime Blenheims, should your subject be one, may have had the same teardrop observation blister endowed side panels as the Bolingbroke IV, IVC, and IVW.
Further back on the fuselage spine between the roof hatches, the maritime Bolingbrokes had fittings for a DF loop football and the aerial mast. the grab handle arrangement and rear cabin hatch fittings may have been different here as well. The Pima pics show a 100 percent authentic Bolingbroke IVT arrangement here, with the possible exception of the anti-collision light, for ref purposes. The air dam ahead of the turret was a late-production (starting during IVT porduction IIRC) Bolingbroke feature.
The turret on both Bolingbrokes and Blenheims advanced through at least three models both on the production lines and in the field. External difs were mainly in guns but internally the drive and ammo handling mechs were modified substantially. The shape on the Pima example appears to be the simplified affair used on Bolingbroke TT conversions and not an actual "shooting hardwared" turret.
Under the rear cabin, the Bolingbroke had a hatch offset to starboard adjacent to the wing root t/e. I'll have to compare in manuals later to see if this may have also been a Blenheim feature. Maritime-tasked Bolingbrokes had a flat circular vertical camera window in this hatch. This was changed to incorporate a drogue launch chute on TT conversions. The trailing aerial fairlead was moved from its Blenheim position to the rear / port of the gunner's position to one nearly under the radio operator's (the new crewman) station just over the aforementioned hatch. The radio operator had a small "porthole" window in the fuselage looking over the starboard wing root. This is often touted as being the main difference between a Boly and a Blennie.
If you have reference cockpit photos / drawings, make sure they are Blenheim ones if this is important to you. There are a number of differences stepping through the various marques of Bolingbroke, but besides the instruments (which also led to a change in pitot head type, BTW) the most extreme difference you'll see between most "Blenheim restorations" and actual Blenheims is in the engine / throttle / prop control yoke: to the pilot's left on Blenheims vice to the pilot's right on Bolingbrokes. I believe this was done for quick-conversion dual control trainer purposes.
Any riveting / fastener artifacts along the wing and tail leading edges should also be considered with caution if using photos of museum restorations as references. The Bolingbroke had an extensive pneumatic boot de-icer system. It was installed on all maritime ops examples, but not on all T / TT examples. However, the fittings and/or structural provisions may have still been in place. I believe this is minimal (vertical tail only) on the Pima example as it was usually cleaned up on late-service T and TT Bolingbrokes.
I'm sure I've forgotten some stuff w/o the material here in front of me. Don't hesitate to poke and prod as your project develops and the wants and needs pop up.
Hey, if you're bent on a Blenheim IV and feeling particularly Canadian-esque about it, you might look at a 404 Squadron IVF. 8o)
I've a slow-cooker decal project in the works to cover the squadron's Blenheims. Might add some other Coastal Blenheims as well... depending on how it fills out.
Cheers from the Great White North!
Terry @ SkyGid Studio / Aviaeology Publishing /CAHS Journal