Thanks Researcher for the great info.
If I understand correctly from some of your previous posts, the "28" and "60" on the barrel lugs equates to 328 and 360 # 8 shot in a 30" circle at 40 yds. I think that would be modified and extra full even though both chokes measure the same with my gauge. I guess the tighter bore may have been opened up some?
My homemade bore gauge measures the chambers at 2.67" so I think they are the factory standard 2 5/8"
Your comment regarding the butt stock style made me wonder if it was a replacement, so I checked under the trigger guard and found the correct serial number. (339334)