I use boiled linseed oil on the rifles that were originally finished with boiled linseed oil. M1 Garands, or other antiques.
Boiled linseed oil, as a wood finish, has a very long track record. Centuries old.
The basic application process is to wipe it on, and wipe off the access. Do not leave access oil on the wood or it turns gummy and sticky. The old rule of thumb, and it’s a very old rule, is once a day for a week, once a week for a month, once a month for a year, once a year for life.
Yes, that’s a lot of coats, but the the finish actually polymerizes inside the wood. It’s not a surface finish. It’s a penetrating finish. It takes quite a few coats before linseed oil offers any substantial protection against water.
The linseed oil will darken the wood considerably. Especially if you follow the above regimen.
Lindseed oil is a very traditional, non-glossy, gun finish. I’m not sure that’s what Marlin put on it at the factory, however. I think a Marlin of that vintage came with a form of varnish.
So, the wipe on polyurethane would be a lot closer to how the rifle was originally finished.