If it has a JM stamp, no extra button safety, a lever, clean screwheads, and hasn't otherwise been monkeyed with, you'll have a good gun.
Some of the best guns in my possession were butt-ugly POS's when I bought 'em cheap... but they had good bores and clean screw heads, so nobody's been inside, and at least swabbed the bore now and then. Every one has been a true diamond in the rough.
My personal preference are the pre microgroove guns 1893 through about mid 1950's, but microgroove guns are tack drivers too so long as the bullet fits the bore. Luckily, it seems lever guns are less frequently owner-modified. These old Marlins were working man's tools for the field, not race guns. While I'd never drill and tap a virgin waffle top, there are plenty of nicely executed scope mounted guns of the era available if you're patient. I have a few and they are certainly
worth spending the time to find. Besides, you often get a good old steel bodied El Paso Weaver scope and vintage mounts in the deal!
Unless it was a true gimme gun, the only thing that drives me batty, running screaming into the darkness, is to come across a museum quality old gun, only to turn it over to find Uncle Bubba's name and ID numbers DEEPLY hack-etched on the back of the receiver with a vibro etching pen... and so poorly it was not legible anyway. AUUGHHH!! That's when I wish I had picked up an engraving skill to artistically cover sins of this nature. Gentle scrolls and stipple fills can work wonders.