I've not ever removed a stock oil pan from a 240Z. My question is did Datsun paint the inside of the oil pan or is it just bare metal?

Bare Metal.  Paint would be a contaminant.

Edited October 17, 20186 yr by 26th-Z

Thanks for the quick response. I had heard that Toyota may have painted the inside of some of the Camry oil pans and some oil additives may have caused the paint to soften, peel and clog the screen of the oil pickup.