New oil pressure switch doesn’t fit...318 LA

I’m rebuilding my 318 LA, ‘73 block. The system at the parts store pulled up part number PS10 as a replacement oil pressure switch. The indicator I have is the light, not a gauge.

I brought it home and attempted to thread it in, felt a little loose but it still followed the threads in the block. I started to prime the engine and oil leaked from the base of the switch. I swapped that switch out for a new one, thinking maybe the brass threads were a bit off. Same thing with the new one, I could actually “walk” it into the block without threading it in.

Of course I can’t find the old one that I pulled out of the engine when I disassembled it.

The bore in the block for the oil switch measures .395. Has anyone had this problem, or know if a part number for a pressure switch with a larger diameter male end?