It seems to me, the "new" .460 Rowland cartridge is a rehash of the .451, and if the Rowland and .45 Super are suitable for conversions from .45ACP, then just about any .45 should do. Personally, I would stick to guns that have their major components made from machined forgings; but the original Detonics .451's were made from castings, so who knows?

The Scoremaster was offered with a 6" barrel on a standard-length slide, but I don't know if there were any guns offered with porting already done.

You could probably get a .45 ACP barrel, with a competition-style compensator already fitted, for what it would cost to buy a 6" barrel and have it ported. All you'd have to do is then ream the chamber to proper depth, and you'd have your "ported" .451 barrel.