Putting the gauge next to the pump tells you the pump is ok..but that's all123-jn wrote:The oil pressure gauge is in the same hole as the sender below the water pump, perhaps it would be worth trying it in the other hole inbetween the pushrods to see if the pressure is ok in the gallery there.
It won't tell you, for instance, if the oil filter is restricting flow.
Gallery pressure is the last point of pressure on the circuit, from there it runs into the rockers
You're looking for 40 psi at 3500rpm with a hot engine