6mm Rem will fit in a short action, but you have to be careful about COL. If it is a bench gun and want use the heavy bullets, and seat them long for more powder space, you could run into problems if you get past ~3.0" or so. At COL of 2.8" to 2.9" works fine in a short action.
The Marlin by all accounts is a fine accurate rifle, I enjoy my Savages, others like Remington actions. With the right tools, swapping barrels and headspacing a Savage or a Marlin can be a DIY affair.
Both of my Savages shoot 1/2" groups, neither one had had any action work. One has the factory barrel and is pre Accutrigger (24" Model 110FP .308 Win) one has a McGowen barrel (22" Model 11 .358 WSSM). I didn't do it myself, I sent it to McGowen and they installed the barrel.