Turns out I didn't have the bolts I needed to get the engine on the stand so this weekend's pretty much done for, so I cleaned the parts a bit instead.
The flywheel mentioned in the post above, I did clean it because it is needed while making the custom wheel; I'll still stick to old setup, even if it puts severe limits to output... I'll look into it after I get the the engine done. My budget wouldn't hold doing both the engine and gearbox at the same time.
Anyway, here's the flywheel after acid treatment:
The brownish tint was picked up after treatment, I shouldäve sprayed it with protective oil but since it going to be handled at the machine shop, I didn't want to. Anyway, the acid does a pretty awesome job. It's phosphoric acid based, so it should leave a phosphate film that will protect it a little bit. The friction surface is spoltchy, probably has foreign particles a lot in it, etching is merciless with those.