Dr. Brown, to be honest, there is no such thing as a "transitional" gun in reference to either a Regular frame and a FW frame gun. It is one or the other. The only thing that will fit are some of the screws.

Another way to tell is the bottom of the gun, the part of the barrel that goes into the receiver. On a FW frame it will be 11/16" long, a Regular frame will be 1 3/16" long, quite a difference.

David