Oil and fuel are fine, no dilution. The truck is a Canadian-built 49 Chevrolet but the source of the pressure gauge could be from anywhere.
A second gauge is one of the options I am going to do.
As far as it always reading 30 I am almost certain because at the time I thought it strange also. The only other time I can recall the pressure drop was after a very steep climb in low gear. When I got to the top the pressure dropped.
Nice to know that the 235 does drop. If I go by the gauge it drops (in my case) about 15 pounds.
I have always been a fan of multi-grade oil but maybe a straight weight might show a difference.