Looks like the alt even has a separate clutch too. Technically a primary shaft that drives no power, only alt and receives starter input. Whacky design. Lots more parts to fail.
The loud clunk says most likely the issue there, the clutch itself, when they get old they can semi-lock up to then release under load and then the loud noise. May slip after or later go back to working. If alt still driving then chain is fine. Yes, most likely cases have to split to get to clutch, although I did a 550 way back by pulling out primary to drop starter clutch into oil pan area. That one though had a wide open pan, this one if like pics shows a pretty much closed up upper above the pan, can't do it.
First pic part #3 has usually 3 rollers backed by 3 springs, you can barely see a couple of them in the pic. Part #1 then slides inside to provide a cylinder for the 3 rollers to work against, it's a common one way clutch, correct it should not slip the other way at all. When it tries to lock up but one roller because of wear slips to drop off, it makes all kinds of racket popping loose, sometimes some pretty loud bangs. The springs wear out pretty quick too and more slippage/inconsistent lockups from that too.