Funky oil pump cover and two plates.

[b4black]

I pulled this off my motor last night. I saw it had a ¼" plate, so I figured it was high volume pump rebuild. I wasn't expecting the second ¼" plate. I guessing the odd angle of the pressure relief means this motor originally came from a Turbo Rivera.

 

[Lockman]

I installed a Melling Thrust Plate repair kit on my '84 (9) a little while back. I learned from searcing on this forum, that the OEM plates were a common wear point. Brought my cold start Oil pressure up to 60 PSI, my cruising PSI up to ~30, & my hot idle PSI up to 20 from ~ 12 PSI, in which I was concerned with. Needless to say that I am very pleased with this . Your Pic's look just like mine from my regal Engine ?
I'm not an expert on these, but I myself, haven't a clue why there would be 2) 1/4" thrust plates ? Perhaps it's the engine type of your 231 ?

 

[ek02]

The open one is for a high volume pump which uses longer gears. The other one is the thrust plate.

 

[WarWagon]

^ correct. Cover is from a Riviera like you thought Rich.