x5 - measure chain stretch properly then report back. The eyeball method is good enough to get you started. I don't think you can turn a 60x crank 20* independently of the cam/s and not have valves hit pistons. The tensioner isn't a factor when turning the crank clockwise by hand. The crank pulls the chain over the IP and cam. There's no slack in those spans when you turn clockwise. The slack between the cam and crank can flap away without affecting valve timing. The dynamic of an engine running on its own changes things considerably.

Here are some pictures of actual engines to help you eyeball cam timing - Timing Chain Stretch//1987 300SDL

Rolling in a new chain isn't rocket science but there is some art. Guidance for a 616/7 engine is 95% of what you need for a 601/2/3. If the chain is stretched beyond spec, certainly if to the tune of double digits, replace the cam sprocket as well.

Sixto
MB-less