Thanks for the replies so far, You've convinced me not to bother with enlarging. Seems I was looking at a case of shells thinking it was a box whoops. I think I may just limit this gun to some light dove hunting/loads. Not much of a target hunter.
Now if I could find a good smith to glass bed this puppy...

I had a box of Sportload #6 paper shells that came with the gun from sears, but the box luckily has a warning against using them in guns shorter than 2 3/4 inch!!!!

I used 7 1/2 Kleenbore Remington Express "extra long range" in my Field grade 1939 12 gauge (armor steel barrels) last weekend for pheasants. Performed well but I don't know how many Oz that load was or if I was ok, or just lucky? I figured both the shells and the gun were about the same vintage there so I went with it.