Oil pressure

[onixbonilla]

Hi everyone.
We had just assambled a new Gene Berg 2213 engine kit I bought around 1995. All measurements were on expected values. CR is set at 8.6:1. Exhaust is 1 5/8 and carburetors are NOS Dellorto 48 tri jets.
Type 4 oil cooler.
After break in these are the oil pressure values we are getting:
40psi at idle 1000rpm cold
6 psi at idle 1000rpm after 30minutes of running
22psi at 3000rpm operating temperature
At present time have no oil temp gauge
Had read that VW aircooled are low oil pressure but are these values normal? Bentley states min 28psi at 2,500 for SAE30 at 158 F
Oil is Castrol GTX 10w40. As our ambient temperature is always around 90F should I go to oil 40 monograde?
Thanks in advance.