I have a 86 1/2 Nissan Hard Body D21. Sometimes on first start, maybe 15% of the time, it has a metallic rattle which sounds like the chain tensioner to me. Goes away after a few couple mins but also has a very hi idle speed when cold. 200+K miles. Often a week or 2 between starts.

yep, replace the chain tensioner and pray the chain itself doesn't need changing too being that old

Thank you