I had that exact same Mossberg at just about the same time. The adjustable choke looked like a poly choke but it was Mossberg’s version which they called a C-lect choke.
Mine was also in 20 gauge. I had a slight problem in that the trigger had a sharp edge and every now and then I would cut my trigger finger. I guess it never occurred to me to take a file and dress down the sharp part.
I think that I “borrowed” the $38.00 against any wages that might be due from working around the farm, took me 20 years to pay for it! :)