> Answer here is to grab a couple SFF-???? Breakout boards, a scope, and a signal generator.
Yeah, I've considered buying an extra adapter and just probing pins — I don't have a spare M.2 to OCuLink adapter but will probably order a few different models to see if there are any differences there too.
> Another thing to consider is isolating all but the first PCIe lane.
The Pi nicely does that for me ;)