The Trojan 12 gauge was made on the 2-frame, the 16 gauge was made on the 1-frame and the 20 gauge was made on the 0-frame and to the best of my knowledge there was no choice of frame sizes when buying a Trojan as they were all stock guns and only an extremely minute number of Trojans were ordered with any options.
There are Trojans out there that would command high prices both in original high condition and in perfectly executed refinished condition but in my opinion, this is not one of them.