It seems to me that the checkered rib is the only thing that would be "troublesome" about the conversion. Obviously started with a M27 -2 frame, could have been either a .45ACP cylinder fitted, or rechamber the M27 cylinder to .45 ACP.
A Model 26 (Model of 1950) barrel could have been fitted, that would account for the barrel marking, but then the rib would need to have been checkered, as I believe only M27 barrels got that. On the other hand, a M27 barrel could have been re-bored, and that would account for the checkering, but then the original barrel marking would have been removed and the barrel remarked. In either case then throw in a reblue.
I'm inclined to think a Model 26 barrel was used and checkered.