Howdy,
As Bullmoose says, yes, it's SASS legal. But, Marlin warns against shooting their old hammered pumps. The locking pin that holds the bolt in place can shear, and if that happens, the bolt comes straight out the back (where your face is). Now, Marlin may be covering their posterior with that warning, but these accidents have happened. If you do get the Marlin, have it checked out by a competent gunsmith who has experience with the Marlin pumps.
Bellicose Bill