Chiphead,
This picture is from the 1961 Chevrolet shop manual.
Oil Pump - Distributor drive cutaway Notice the thrust washer between the bottom of the distributor drive gear and the machined end of the oil pump shaft housing. The cam rotates counter clockwise as viewed which means the distibutor gear is forced down against the thrust washer and hence the oil pump.
Look closely at the distributor hold down. It appears to be flanged downward around the distributor housing and would then only put downward force on the gasket setting in the block. Appears, that the distributor has little if any downward force applied from the hold down assembly.
I would expect there to be a small amount of end play in the distributor shaft when installed in the engine. i.e. clearance between the distributor drive gear and the distributor body. If the distribtuor body was pushing down on the gear, then I would expect to see what happened in your engine.
I'll plead ignorance on what the plastic washer is for.
I think the cam in my 235 was a Howard's. It's been 25 years since I did that project and I'm getting a littly hazy on some of the details.
