I have my dad's Glenfield Model 60 with squirrel stock, made in 1972. I liked it as a kid, but it always had problems with feeding: jamming, mangling bullets, etc. I moved away, years passed, my dad passed away, and then I thought I'd figure out the problem and get it working properly as a memory of him.
So... it turns out this time period (1970s? I don't remember specific dates but you can look it up) had a really bad design flaw: they had a 2-piece feed throat (split down the middle, lengthwise) that would spread and then there would be malfunctions with feeding. But later (in the 1980s?) Marlin replaced this with a one-piece feed throat that you can get and retrofit to guns with the old 2-piece type.
It only takes some simple modifications, the most involved is due to the fact that the new feed throat has 4 lugs that attach it to the action side plates but the old 2-piece only had 3 (which probably did not help things). After my past experiences with this extremely frustrating problem, I wanted the feed throat to be as stable and locked in place as possible so I drilled a 4th hole in the side-plate for maximum engagement of all 4 lugs. I mention this because some people just grind off one of the lugs from the feed throat, and then only have 3 lugs attaching it to the side plates. I much preferred 4 lugs so I drilled another hole. I also had to reshape some of the feed throat with a dremel to work with the bolt of my gun (not the feed ramp part but some of the side structure). I suppose you could also replace your bolt with the type from the newer guns but I didn't see any reason to do that and just made it work with the existing bolt.
Anyway it was a completely successful project and I have never had another feed malfunction. So if you have one from the 1970s and have feed problems, maybe take a look and see if you have the 2-piece feed throat and think about upgrading to the reliable 1 piece.