I usually set the timing marks on the gears on a work bench before installing, then carefully bring it to the engine without letting it skip a tooth... Put the crank gear on the key way and then turn the cam so the key way for the cam sprocket lines up...
Then check afterwards to verify the timing marks are properly lined up after installed up on the engine...
Especially with no heads on the engine, the cam will turn freely so you can line up the key way with the chain set to the sprockets...
