get some acetone and ATF, mix both about equal. WD40 is nothing infront of it. It will creep and loosen anything.
Get a table, put the bike up on it so you can work on it whilst standing, buy an impact driver with bits a large hammer and get to work. Everything will come out, for the chain sprocket removal, wrap a rag on the gearchanger use a vise grip to select a gear, get someone to sit on the seat and load the wheel, take a giant breaker bar and undo the nut.
are you just doing a customary cosmetic resto or are trying to bring it back to 1980s quality brand new spec?