Phil,
While I'm all for the least invasive method to a solution I don't believe you'll find the piece of mind in having really isolated the problem unless you pull the motor out. You stated that the PO had the same issue with low oil pressure after the main bearing caps being shimmed, maybe this wasn't the right answer to the problem. I don't think you'll be happy until your able to mic the crank and bearing completely.... Just my thoughts. The rocker arm situation is a head scratcher there are a lot of issues going on with all the different parts.

The plus side is being able to clean up the engine bay and paint the block, I'm sure you'll find some other projects in there as well. Good luck, I'll be following.

~ Craig
1958 Viking 4400
"The Book of Thor"
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1960 Chevrolet C10
"A Family Heirloom"
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'59 Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)

If you don't like driving yourTruck, you won't drive yourTruck..| Living life in the SLOW lane