Good evening yall. I've been helping my brother get his '94 B2300 running again, and I've ran into a roadblock pretty much. I'm gonna try and lay down all the information on the issue so hopefully someone can help us out!

The issue began suddenly a few months ago, we were driving back and suddenly heard a lot of top end noise, and the oil pressure dial dropped. Limped half a mile back home, its been in the shop since. Here's the list of the things we've tried:
(1) Changed the oil.
(2) Dropped the oil pan and removed the oil pickup. The seal was still brand new, no contaminates were in the oil or pickup tube.
(3) Retimed it, broke a tooth off the flywheel when we missed it by a tooth or 2. Replaced the flywheel and clutch.
(4) Replaced the oil pressure switch, just incase. No difference.
(5) Verified the filter is good.
(6) Cranked motor with the pressure switch removed, no oil came out of the block.
(7) Inspected under the valve cover and the crankcase, no damage or metal filings to be found.

Couple more things that might help, she still runs but we haven't let it go for more then a minute (would suck if we melted the cam!). The previous owner directed us to the camshaft synchronizer, he said he replaced it once. I'm not sure if that would affect the oil pump, if anyone knows more about that please lmk! After draining the oil, when I removed the pickup tube it was full of new oil(so some must have been sucked in at some point!). The noise is a constant top end knocking, sounds exactly what you'd expect from an engine with no oil in the top end.

My only answer is the oil pump, however I've never heard of an oil pump grenading or otherwise failing instantly so I'm trying to avoid replacement for now. Truck only has 169k miles too. Any help or insights would be appreciated! Thanks.

Edit: Previous owner mentioned something about a pin on/or has something to do with the cam syncro that may have failed. I am not very familiar with this motor so I've no idea what he may have meant.