Glort,
Don't worry about getting the keys back in right.
Before you refit the flywheels clean the keyways in the flywheel and the shaft out with the edge of a file then clean up the keys on all four faces, keeping the bottom one as flat as possible.
Cover the top face with the ink from a black or dark blue permanent magic marker - Sharpie or what ever they call them down you way, then tap it lightly home, withdraw it, file off the high spots, where the ink has been scraped off in the fitting to make them a little larger, repeat until you've got about 90% contact then drive them home hard.
After they're in use the pen to make a 'witness mark' in the keyway, about a millimetre outboard of the head. if the gap disappears you know there has been movement.
If you still have doubts put a Jubilee (hose) clip on the shaft, up against the key, it won't stop it coming loose but it will stop it dropping out and letting the flywheel run wild.
Finally, rock the flywheels back and forth each time you hunt for lift of the exhaust valve to engage the decompressor. You'll feel the slightest play straight away, ask me how I know!
Cheers Stef