If, perchance, do add swivels, know that there is a correct location in the stock for a butt swivel. DO NOT attempt to use the Marlin Bullseye as a location! The correct location can be determined by looking at a Marlin with factory-installed swivels, usually an inch or so below the Bullseye (towards the butt) Having been a professional gunsmith for 40 or so years, I have replaced A LOT of the Bullseyes that owners drilled out to install the swivel stud and reinstalled the swivel in the proper place. It is preferable to use a drilling fixture like the B-Square to drill the hole, then counterbore a bit so the aggressive threads of the swivel doesn't "pull up" the wood around the hole. I always used beeswax on the threads, lubricated the threads going in & seals the hole in the wood. A drilled out bullseye effects the value of the rifle. I tried several times to get one of the Marlin-branded carry straps on eBay, some had reserves in excess of $100. I did get one un-branded strap that I switch between my 39a's, still looking!
Phil
NRA Benefactor Member