Thanks for the replies.
I'll try the 0000 steel wool before I resort to sandpaper. I'll definitely be gentle either way.
The stains might be too deep for magic eraser, since the cabinets seem to be pretty much bare veneer. I'll give it a try though.
One originally came raw wood, and the other was oil finish, but at this point the finish on each seems to be non-existent.
I think I'm going to use Boiled Linseed Oil to replicate the original finish once they're prepped.
BTW, does anyone know which crossover this is? I have K33P Woofers, K55V Horns and K77 Tweeters. 1972 vintage vertical horns.