The headers are as much for ease and conveinience as anything. They are literally hard mounted to the flexpipe in the dyno cell since 90% of our stuff is street FE builds. The engine is going overseas into a Mustang convertable, so the comparatively restrictive headers are probably kinda realistic.
The target power for this was under 500, so we were ahead already and no real reason to flog the death out of a fairly mild customer build. The intake and single carb were spec'd out in the build as a matter of performance versus cost. I suspect that a pair of carbs would pick it up nicely but break the context of the project in terms of cosmetics and cost. A modified set of heads would also pick it up a ton.
Exact pricing is somewhat touchy in this tech portion of the forum, as a courtesy to the other builders here. Strangely enough, an awful lot of us have names starting with "B"....
. In any case its probably safe to say that it costs about 4 or 5 grand more than a comparable 390 stroker build due to the cost of the block. Middle 'teens...gets you an extra 37 cubes and maybe 40ish extra torque & HP coupled with 100 less weight.