I've recently rebuilt mine. The little diecast levers are splined on but will pull off if you are careful. You will need to mark the position and take a photo of each end so you have some reference. I rebuilt a second unit so had my original for reference and spares. The other ends are held on with small press on spring washers that will also prize off if you use a tool that hooks under to release the teeth from the shaft.
I used various thicknesses of neoprene wet suit material to replace the seals on the flaps as the cloth surface sticks well to the contact adhesive and should make the sealing surfaces last well. 3mm and 6mm if I recall correctly.
There are three levers that are mounted on posts that are crimped in place in the box. The levers are held on the post by the end of the post being knurled over. Removing the lever from the post also strips off the knurled-over lip.
I was planning to drill and tap the posts to take a retaining screw and washer, but anyone have any other suggestions.
I am having a hard time deciding whether the cable nipples were originally zinc plated or whether they are a low grade stainless. Some are as new, others have a tough layer of corrosion on them. It may of course be dependent on year, mine being a 1963.
Masking and painting around sounds like a reasonable idea! I always go overboard (ask Enigmas), and so have stripped all the internal moveable flaps and grit blasted the cases inside and out.