I use Steve Rose, Rose Action Sports in Pembroke, KY (gunsmith@roseactionsports). He has cut, crowned and re-threaded barrels for 11-87, 870 and the M1 Super 90 (cut to 13.5"). Choke tubes will have to be Tru-Choke (standard, not Thin Wall) because of the barrel thickness. I couldn't find anyone who had the tooling to rethread for the original choke tubes.