I have a copy of Remingtons' booklet of instructions and parts list. It looks to me as if the magazine on a 11-48 is a press fit. The info you have is correct as it being part of the receiver assembley. The magazine tube on the M-11 however is a separate piece threaded on each end. Don't know if this could be adapted to the 11-48. You might try contacting Remington however you would probably be better off contacting a local gunsmith. I've never had much luck with Remington except visiting them while they are at the Grand, where they have a few gunsmiths in attendance.