Have a 1 cylinder air cooled engine(800G) that had to remove the camshaft and forgot to mark it's placement. What's the correct way to get it timed cam to crank? see no marks on either. Didn't know if the key way for mag on the camshaft goes a certain way to the key ways on the crank??

Piston at TDC
Camshaft positioned with exhaust valve closing and intake opening. Next time piston comes to TDC both valves should be closed and the magneto should fire the plug and away it goes.

I’ve never seen a stock engine that the valves “rocking over” or overlap period wasn’t centered at piston TDC. Magneto on flywheel will usually fire the plug every time piston comes to TDC. This is called wasted spark design on multi cylinder engines but all common single cylinder engines do that too.

A separate mag driven off crankshaft may have gear reduction so that it only fires at TDC of compression stroke so that will take some timing.

Magneto driven off camshaft will need timing as well because it fires only every other time piston gets to TDC