All three of mine have the same 'viewing port' safety selector (upper photo), all are marked Field, all are double trigger and all are of a common pattern regarding number of screws / pins and locations and the cut of the stock & sideplate.
The 12 ga has one difference on screws, at least that I have found, in that the screw just forward of the trigger guard is not tucked under the curve of the trigger guard as much as the 16 or 20.
Of the three, the 12 is more the oddball, aside from having been reworked and I'd think restocked & reblued. The 16 and 20 look like they could have been made on the same day and lived together ever since.
I'll get photos up or off in the next couple days.