Very cool!

Knobs, thanks for the great pics! This rifle has a combination of details I haven't seen before.

As I previously mentioned, Diana's "big" sporting rifles--models 25, 27, 35, and 50--seem to have undergone a major simplification sometime around 1964 or 65. 27's made after this time typically have the familiar stamped steel trigger blade with small exposed adjuster screws; click-adjusting plastic rear sight; rear sight/scope dovetail; and non-finger groove stock. Your gun has the last style of trigger used before the "big change," which was basically a plastic copy of the previous solid alloy blade.

The dovetail-mounted stamped rear sight and leather (?) breech seal, are other details I associate with "pre big change" model 27's. BUT, the clamped hooded fixed post front sight, and breech jaws without the flat area on top, are "post big change" details. All of which proves that all these things did not happen at once, I suppose.

Another interesting detail is that the trigger has only one screw in it, I would assume this is the sear adjustment, with the usual additional lock screw omitted? I'd never noticed that one before....perhaps the plastic was deemed to generate enough friction that the lock wasn't needed.

So I would guesstimate its production date as between 1962-65.

Question by the way: does it have a wedge or ball-bearing breech detent?