Dunno which finish was used on it, but I'd sure recommend a chemical stripper rather than sanding. Might have to experiment a little unless someone has firsthand knowledge about that particular finish.
But when it comes to the checkering, I've had the best luck using a fairly stiff nylon bristle brush. It seems to work best when the stripper is still a little wet, yet the finish is loosening. Might take a couple of treatments, but you can readily remove the finish that way without damaging the checkering.
Nice score on an interesting little rifle. I have a short 58 (different model and brand, but similar dimensions), and it's become just about my all-time favorite gun for close, quick shooting.
Yeah, yeah, I know- I've heard all the talk that long barrels are cooler and "just as fast to handle." Bull patty pie! Long barrels don't belong in Alaskan alder patches. Got them and tried em repeatedly. The shorties are king until the terrain opens a little.
Looking forward to how that great little gun turns out. Looking forward even more to your hunting reports.