If it's going to be a dedicated slug gun you might consider shipping it to Dave Klotz in Weedsport, NY at Da-Mar Gunsmiths. Dave has some patents related to making slug guns shoot. Brownells and others carry his stuff.
He specializes in Remingtons. He can pin the barrel in place so there is no chance of movement. He also makes a rail scope base that sits on the receiver like a saddle so the screws go through the curved side of the receiver and not the center of the top which is much thinner and prone to recoil related failures.
Every one of the guys I know who have had him dance on their slug guns (that can shoot...) are getting groups of 2" or a less at 100 yards.
I don't know what the work costs but he has always been very reasonable in his pricing for my work and folks send him guns from all over the US and parts of Canada. His number is (315) 834-9156
Lance