In my L134 Go Devil you can change the relief pressure (and to a point, system pressure) by shimming the relief spring in the pump.
I'd still stay within specs as increasing pressure does not necessarily increase flow.
Someone said CAM bearings can cause low pressure... I believe that its mostly main and rod bearings. Cam bearing generally don't wear nearly as fast as anything connected to the crankshaft.
Also, as noted, using a heavier weight oil will bump pressure up... but again, you really want FLOW... a thick oil may read as high pressure on the gauge, but not be flowing anywhere near as fast as needed.
Stick with 30 weight oil, the book says as long as you read a non-zero number (like 2-3psi) at idle you are good. If it drops then consider new main/rod bearings as they are the real culprit.
