my guess would be that many times the "spare" cylinder ( in this case it would have been the magnum cylinder) is the one that is stamped with the last 3 digits of the guns serial number,so there would be no numbers on the 22 lr..........usually the short 4 5/8 in and the long 9 1/2 inch guns are the scarcer of the line, especially if a 200th year gun and in stainless steel.....
a letter from the factory would tell you "how" ( what model/catalog number) the guns was shipped as, but I'd bet it was a convertible all along.