ball bearing oil valve

[mac92a2002]

Hello folks looking for some help. I'm build a 90 an z32 engine for my z. So I've got the engine torn down to the block and I have found what I think are two ball bearing check valves where the oil filter housing goes. One is there the other is torn open and missing the ball bearing. What are these for and where can I buy a replacement. Thanks for the help.

[DCaff300ZX]

The ball bearings are check valves as you guessed for keeping oil pressure, and both need be present and with keepers.
I think that a Nissan dealer would be where I'd start, perhaps Z-1 or Concept Z Performance (and other major Z32 vendors who carry engine kits) may also carry them but I would call on that one.
Good Luck!