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Bertie - my upper OP is within the limits of 10-35PSI.
It's my OP at idle that concerns me.
Specifications for the A-65 show an acceptable range of between 10-35
and I'm concerned I may be below that range at idle ( at operating
temp).- Mike

Do we all agree that a pressure relief spring probably will not figure
into the fix for the problem of raising my OP at idle? - Mike

As the engine ages the pump wears and pump clearances open up so that
it pumps less volume. The bearing clearances also increase so oil
flows through them easier. The result is a drop in oil pressure. This
shows up more at idle since the pump puts out the least volume then.

As the RPMs increase, the pump puts out more volume and the pressure
builds until the pressure relief opens up to bypass the oil flow to
limit the max pressure to 35 PSI.

Even on a new engine, the pressure relief doesn't have much effect at
idle since the pump is not putting out enough oil to build the pressure
up enough to open it. If you have 35 PSI at idle when warm something
is wrong ... probably not enough bearing clearance.

The solution to the problem is to go to a slightly thicker oil that
doesn't flow through the increased clearances as fast. That lets the
pump build up pressure easier at idle. Don't go too thick or it can be
a bad thing if the relief can't hold the pressure down.