Scary Random Engine Clank/Tap

[Chickenstrips]

So I just bought a 1973.5 coupe with 118k miles or original miles. After a good clean up of tank and lines, fresh oil I got it started, but it makes an intermittent sound like a small hammer tap/clank on the case, but only on deceleration and idle. At a steady rpm it sounds perfect, its only when I let off or at idle it makes the random loud clank sound every 2-10 seconds.I am looking forward to doing a rebuild, but was also kind of hoping that it's something to do with cam chains so I can upgrade and drive in the spring when roads are salt-free and get to know the old tired engine before rebuilding. I took the cam chain covers off hoping to see an obvious explanation. I have read all threads but can't say for sure what I see. I think the left side looks stretched because of the smallish gap between idler arm and housing? It does not take a lot of force to deflect the chain 1/4". Also left tensioner piston looks more extended and possibly near end of travel. Any input from experienced eyes would be greatly appreciated!! thanks

ps. I have video of first start and clank but its 4 min long and figured too long