question on distributor '68 383

They were common on industrial motors, pumps, etc up through the 70's. It might be threaded in similar to this:
Screw in Replacement Partridges Bottom Bracket Oil Cap Oiler Point for BSA Frame | eBay

From your pic, it looks like you could reclock your intermediate shaft CCW a few teeth for better access. you'll need to retime the motor of course, easier if you can track how far you turn it.