Technical Oil pressure dropped to zero on start up...

Who's filter was in there, FRAM?

 

Most (all?) filters have a bypass feature to allow flow if the filtering is blocked. I can’t understand how all flow was blocked. Was it a canister filter? What does the oil in the pan look like?

 

I posted /mention this issue in post #4
426 Hemi
I have Heard of quite a few times after oil filter removed / changed .
No Oil pressure.
Older Diesel would do the same on fuel filters, lose prime .

 

This is pretty much impossible on an early hemi unless you've converted from the stock canister type filter.

The early hemi has an oil filter bypass built into the block. Some folks block this safety feature with a plug (see image). If you do this, BE SURE that you use an aftermarket filter adapter and a filter with a bypass in it. The original canister style DOES NOT have a bypass, so if you intend to retain the original canister filter DO NOT block the original bypass system in the block.