How about the screw hole spacings: (1) distance between the two screws through the front part of the trigger plate, and (2)the distance lengthwise between the two front holes and the front trigger guard threaded hole?
If the screw hole spacings are different as well, then there is no hope of adapting a 12 gauge trigger plate to a 16 gauge receiver.
I do have a complete 1904 gun, which has a trigger plate that is slightly wider at the front end and has two small "lobes" on either side at the front. However, the screw hole spacings, mentioned above, are the same. Therefore, a (my) 1904 plate could be made to fit a (my) 1902 type gun, in 16 gauge.
