The Models 80 and 81 were produced at the same time. The 80 has the detachable box magazine, and the 81 is the tube magazine version.
My Model 80DL is pre-microgroove, with the peep sight - a very accurate shooter! No scope grooves either - they came in about '55 or so.
I like these rifles more so than later Marlins, as they have a heftier stock, more 'adult-sized'.