not a lot of meat over the chamber so most gunsmiths will not do it, one way to do it is to drill thru the chamber tap it and grind the screw flush with the chamber wall, seen a few ones like that. you could also silver solder a steel rail on i have seen them done that way too
as far as shells go i would give the fed heavyweight 7's a try w/ flite control wad or the hevi 13 7's both should give killing patterns to at least 35yds, you wont have big 10" numbers but patterns should be very even.