I had a .38/.45 Clerke conversion a few years ago. Apparantly it was an early attempt to get .357 velocities out of an auto, but the concept failed due to the unsupported chamber. It was an easy conversion since you used a necked down .45 ACP case, so your original .45 magazine and slide could be used without modification. The barrel was a rechambered .38 super. Target shooters picked up on it for a while for used in the Centerfire Match since the bottle neck shape would even feed full wad .38 bullets. Kind of fun to play with although I did lose 10% of my cases in forming them. Military brass did not form well, nor did cases with a channelure on them.
I currently have two .38 Specials on .45 frames. One is a 6" Clark Long Heavy Slide that shoots like a dream. The other is a Springfield 9MM that was reworked. It has Bomar sights on it, so it looks like a hardball gun. The barrel is a fully ramped Caspian. The slide was an early Springfield, so the 9MM face had to be opened up a bit. The magazines are some after market ones that do not have the follower that changes angles as more rounds are loaded into it, so feeding is good for only four rounds. In bullseye matches we only shoot five shot strings so I load one in the chamber, four in the magazine and I'm good to go.
All these conversions are are separate frames, rather than conversions on a single .45 frame.