I am left somewhat confused what the 'ideal'pressure should be at different RPM's. It seems possible to me to add incorrect spring lengths and/or washers, over-pressure and blow a seal or too.

Sounds like a plan. 20 psi hot idle might be ok, but not when the oil is at cold idle. Not sure what you or he meant.

As I mentioned earlier, a shim of 0.160" did not improve the seating but a shim of 0.340" did the trick. The relief valve will not work if the shim is any longer than 0.360". This prolonged cranking to test for oil pressure is doing harm to the cam & lifters.

I fear that the original cam assembly lube has been mostly wiped off by now with all of the cranking. I would fill it with 20W-50 oil & add a large dose of ZDDP. On this side of the pond "GM EOS" or "ZDDPlus" is available. Find something! I would be willing to send you a bottle of ZDDPlus if necessary. I was never comfortable with the "breakin" oil that you were using.

When you first start the engine, hold it at around 2,000 rpm for at least 20 minutes CONTINUOUSLY to get proper cam & lifter breakin. 30 minutes would be better.

This means that all systems have to be ready to go, no shutdowns for leaks or other problems. Have the timing properly set before starting up. If the engine gets too hot during this period, & it well may, put a garden hose in the radiator filler, open the block drain valve, & use this as supplemental cooling.

With luck, the cam & lifters will not have been scuffed yet, you will get a good breakin, & everything will be fine.

I wish you the best my friend.

Regards,
Dave