Nice!
Although you didn't ask, a
Skinner Express aperture sight would be an awesome replacement for that Tasco, which everyone will agree needs to come off.
Most .44 Mag Marlins will also shoot .44 Specials, but some are finicky about cartridge OAL. This can be easily remedied by reloading (see below).
No need to automatically replace springs. A 1981 rifle is not particularly old; the springs are likely to be good for another 40 years or so.
It's an easy rifle to disassemble, which should definitely be done to clean out the old gunked up lube, etc., as well as familiarizing yourself with the guts of the rifle. Your favorite gun oil and grease will work fine.
Figure on 3 MOA, which is probably as good as you can hold with irons. The .44 Mag is certainly plenty for deer-sized critters within 100 yd; many will say 150 yd. Elmer Keith would say 400 yd, and proved it.
Microgroove rifling is quite shallow, so tends to do better with jacketed bullets, but can be equally (or even more) accurate with properly-sized cast bullets.
This rifle is a very good excuse to begin reloading and casting. The .44 Mag is a very easy cartridge to work with. It can be loaded to power levels ranging from kid-friendly "cat sneeze" loads up to OMG level.
We have a
Lever Action forum, and the
Marlin Owners website is the ARFcom of leverguns.