Update: thanks to everyone for the advice. (Toyota Diesels FTW)

480-500 across the cylinders without adding oil, which was way better than I thought it would ever do with 327k km on the clock.
I don't know if doing it through the glow plugs was the easiest. especially with my sausage fingers trying to grab these tiny bolts
Anyways, I will keep hunting as to why it doesn't like 20psi.
Any recommendations for PCV tanks or catch cans?
Also, I would love to hear other ideas about what it could be because I didn't think my catch can was that restrictive it has a 3/4 inch inlet and outlet.