I have a PDF tech manual that has the 660 tiller in it, it covers all your questions, shoot me your email if wanted.
If you're lucky and take all the bolts holding the cover off, then run a razor blade between the gasket and the side of the tiller body
you might get the gasket off and in reusable condition
Silicone gasket sealer is your friend!Another question... even though I doubt they are... are the gaskets on these re-usable? I would like to take off the gear cover for a thorough cleaning, but looks like that gasket is $50?