it would usually say on the barrel , right after the model number like on mine for example , " model 336 cs " , so yours is probably an older one , you should give marlin a call . or you could take it to take it to a gunsmith and have him see what size holes they are , and what he has to fill them

P.S. - i think you should edit your post to take your rifles serial number out of it , that' s not something that you want to divuldge