I don't know if I can add anything constructive, but the answer is certainly yes; post-1913 Field Grade guns were built on regular frames, especially up to about 1920. Also, although one doesn't see an example very often, 16-bore guns could be ordered on Regular frames up to about 1920. Three years ago a gentleman brought a 16-bore Ideal Grade to the Southern that was built on a Regular frame. That gun was in poor condition, but I really like the Smith 16 with the R frame and lockplates from purely an esthetics point of view.