FLAWaterfowler

Considering the new very accurate and hard hitting 20ga slugs out there..Ive been considering an M1 -- but it would have to do double duty as a bird gun / slug gun... Couple of questions... Are all M1s drilled/tapped for scope mounts, or is it just on the slug gun model... If I added a slug barrel to a standard M1 (or vise versa...a 26" barrel to the slug model) do I need to change the forestock? Ive heard that they may need to be swapped out... Anyone use an M1 as a slug gun? A double duty gun?