Usually the oil pressure is tapped into the hole just above the oil filter boss. Some blocks use a larger hole than others. It is tapped standard pipe thread.

Oil pressure readings can be taken from any of the lower left side oil galley plugs. Including the front one.

 

I have a stupid question. Where is the oil pressure sender located on a 1972 402 Big Block Chevy.This block came to me with plugs everywhere. I know it's somewhere next to the oil filter but which hole?Can someone send me a pic if available.

I don't have a pic but the one I use on my 461 is toward the front of the block on the driver side. It is located below and forward of the front freeze plug. That will give you a more accurate indication of the oil pressure to the front main. It is a 1/4" NPT hole.

 

Here's a 454..