A/C System pressures

[jradford]

72 C20 with factory air that was converted to R134A by some shop in Ar. that says on sticker under hood IAW some standard and lists new oil type as well. Done before I got the truck. Not cooling well so hooked up a set of gauges but this being non standard setup for R134A not sure what pressures should be. Looked through the past posts but most just explain how their conversion was done. Looking to find out what kind of readings I should see to determine if I need to adjust the charge. At about 85 deg ambient and probably 65% humidity it is reading 35/310. This would normally indicate a restriction on the low side and an over charge but not sure with the current setup. There are bubbles in the sight glass but from what research I have done it is not an accurate indication of low charge. I don't want to drive the high side any higher. Normal readings on an R134A system should be 45/250 at this ambient temp. but with factory evaporator which is smaller I am not sure. Any recommendations based on what you guys are seeing?