Mtn Hunter you did great on getting that rifle. The 99M1 is tube fed, of course, and its twin is the 989M2 which is box mag fed. The first was made from 1964-1978 and the second 1965-1978. The M2 is seen a lot less often. Someone asked about replacing a stock. Well, if you want to retain the original looks you want the walnut stock with the handguard on top. With some searching you might find the walnut stock. If you do not care about the original looks being retained you could other Marlin stocks that might fit some way with a bit of trimming. Actually, all the M1 is a Model 60 with a shorter mag tube and a slightly different stock configuration. The Glenfield 75 is like the M1 but without the handguard and is non-walnut wood and, of course, does not have the nice rear sight. The Glenfield 70 is like the M2 but without the handguard and is not walnut wood. What I suggest..if you have the money to pay a gunsmith, or can do it yourself, is get either one, or both of these rifles, and do not worry about that factory rear sight. A much better sight is a set of Tech Sights. Only you would have to pay someone, or do it yourself, drill and tap a small hole at the front of the barrel just like the Marlin 60 and Marlin 795 have for their front sight. Then you can put the Tech Sights front post sight on and the Tech Sights rear sight mounts easily on the receiver dovetail as Tech Sights do on the 60 and 795.
The second and third rifles from the bottom in the photo are my rifles...you may be able to see how nice the Tech Sights make the 99M1 look (2nd from bottom) in that makes the gun look even more military, so to speak.