I know some waterfowl guides also, on Md's Eastern Shore. Popular guns with them include the Ithaca 10 ga autos, the older version of what Remington offers, but most parts are not interchangeable. Perhaps your buddy can locate a used one. I know just one guy with the Rem 10, last I heard no probs. I believe the owner of that one uses it for waterfowl and turkey.
I've shot a coupla Ithacas, but not extensively. While it's one bignheavy load to carry(Around 11 lbs!), it balances and swings nicely.They come with sling studs for a reason.And, felt recoil was a lot less than a standard 12 with a barnburner 3" mag load.
IMO, a 10ga auto is a specialized tool for long range,steel shot, rather than a GP shotgun. Secondary uses,turkey and big heavy buck loads for those who cannot use slugs....
They are fun to shoot. Try a few reloads with say, 1 3/4 oz of 7 1/2 shot on handthrown clays and enjoy....