Mike,
I use Castrol 20W50. Pressure is around 20-40 psi at idle (idle is gloriously lumpy), 55-60 psi at speed, warm. Cold is around 60 psi at all engine speeds. Takes a few minutes to warm up as it has an engine
oil cooler.
Pressure gauge is mechanical and input is taken from the block rear center tap above the bell housing just behind and below the intake manifold.
I understand that the indicated pressure may be a bit higher at the tap on the front left side (facing forward) of the block just above where the mechanical fuel would go if I had one, since it's just on the output gallery of the
oil pump, but I haven't checked it there. I use that tap for the ACCUSUMP.
I use a "normal" Melling pump. No high volume, no high pressure, no heavy duty. I'm too paranoid about losing another camshaft and distributor.
This combo has worked in the 521 for 18K miles just fine.
Tom