Patrick - I see Jeremiah responded about cleaning the inside of your gas tank but it sounds as tho you also wanted to do the outside. If you clean the inside according to the FAQ using muriatic acid then I don't think you have to worry about gas fumes when cleaning the outside. If you're not doing the inside of the tank, and only want to clean up and paint the outside then I get very scared using a sandblaster since there will still be gas fumes and the blasting does heat the metal, and cam even make it brittle. I don't know what would happen and would NOT recommend sandblasting the tank. I met an old timer one time that brazed leaky tanks and he filled them with water. Even that bothered me since there had to still be fumes - so I never really understood how it would work. I've always been extremely cautious when wire wheeling the outside of my tanks. I would clean out the inside as much as possible with some type of soap and water, or other non-flammable liquid, and then proceed to the wire wheel method. Even a wire wheel will get the tank hot so I'd proceed at a slow pace and allow cooling. I'd also be ready to use a good cleaning solvent (kept a long distance from your work area) and some primer spray paint since the tank will immediately begin to show some surface rust (at least mine did).
Now, on your clutch assembly, I'm not one much for clutches (as my name may imply) but based on the few I have done your drive shaft certainly would seem to be reusable to me. I wouldn't bother sandblasting, I'd use a wire wheel again, or even just sand paper to clean off the paint and rust. I'm not sure about repainting it before it's all reassembled. I'd probably wait until you have the assembly together and then paint the entire assembly. You'll have some grease and oil on it so some parts won't paint well, but since it's mostly hidden and this is a worker I wouldn't be concerned. As far as the question on that ring, I can only assume it's part of the bearing. I don't think there would be anything like that for the spring spacer, but hopefully some Gear Heads will chime in here.
Good luck with your project.
Hydro Harry
Old Cubs Never Die (and hydros require less maintenance)