If you end up with a prophet 30 and want a slug barrel for it, find out the appropriate twist and preferred type of rifling and buy a barrel blank. Then have a good machinist duplicate your 30 barrel with the blank. I have had Paladin Machine Service make several suppressor mounts ,two barrels, and misc. parts for me. Top work, fast, and the one thing you can never find with quality - cheap. I'll guarantee he will do a perfect job cheaper than any other qualified machinist you will ever find.
He has done a lot of work for some of the big names in AR development, and has a strong reputation. I live close enough to him I just drive there, just over an hour one way. He is retired from real job, and just does machine work to supplement retirement. Lost his FFL in the Carter years when the feds drove most "kitchen table FFL's" out of business. He couldn't get the county to rezone his workshop as commercial to keep it. Blame the liberal neighbor for complaining at rezoning meeting.