Perhaps a mite more specific answer, at least in part. Yes the two guns are actually the same gun. There may or may not be differences in the roll marks on the barrel.
Yes the gun is larger than the Cattleman. No, the gun is smaller than the Super Blackhawk. It is sort of the size of a Blackhawk but if you ask for leather for a Blackhawk, the gun will rattle around in it.
Suggestion: Use a local leather maker. Or, make sure you ask ANY maker if they have a pattern and/or mold for the Buckhorn. They probably won't. If your maker can getcha close, the holster can be blocked to fit. Best bet is to have your maker make the holsters to your guns. Unless ......
Suggestion # 2. Holsters to fit the Original Vaquero should be just about the Kats Meowe. I would expect Vaquero leather to fit the Buckhorn to a "T" If you would like, I can confirm that for you. Simply send the guns to me, and I'll trial them in my Buscadero rig that was originally built for 45 Colt Vaqueros. It shouldn't take more than a year or two of testing to confirm the fit, pro or con.
Some refer to the .44 Mag as the .44 Russian Extra Long. Once you receive your guns, I'd like to suggest .44 Russian cases with your favorite (or soon to be favorite) BP or Sub, topped with a 160Gr bullet. a very nice pleasant load you can shoot all day and with the added weight of the Buckhorn soaking up even more of the recoil, a real FUN pussycat.
Most folks you shoot with won't even notice the difference in size
Coffinmaker