Edited to add: Gabe just came in from (where else?) running trains and strongly suggests you use an old toothbrush and Goo Gone, or your cleaner of choice, to clean the worm gear on that 681. Old grease and grit will tear that gear up and, while you can replace it, it’s better to scrub, blow dry (air compressor or cold air from a hair dryer) and fresh grease.
You have good advice so far. I’d add that since it’ll be your first disassembly, take lots of pictures so you remember what goes where. Work on a big, smooth, light-colored surface (you’re going to drop stuff anyway, but don’t panic; most tiny parts are replaceable, but you can find most stuff on the floor by turning out the lights and having a kid shine a flashlight across the flooring.)
Did anybody clean wheels in the 1950s? Also, did anyone ever check brushes or clean brush wells? Yeah, that’s what we thought too. If the brushes are worn, a couple of bucks will replace them. While you’re there, ask for the right kind of oil. We boomer kids were good about greasing stuff and not good about how much or where. Dan isn’t kidding about the cement-like grease. Toothpicks are soft enough not to scratch and small enough to get into nooks and crannies. Pipe cleaners aka very small chenille stems are good for smoke units and brush wells.
Don’t clean anything with steel wool. It comes apart, whether you realize it or not, and it’s really hard to get rid of.
Most of all, enjoy.