I have made my own adapter for a standard fuel pressure guage. All I did was cut off and un-bolt a fuel line from a fuel rail on a 4cyl 91 camry (easier to find and I dont feel as bad cutting them up). I hose clamped the line to the guage and connected to the fuel filter to get the pressure reading there. I also unbolted and cut in half a cold start injector line from the same camry, bolted that to my fuel rail and hose clamped that to the guage to get a fuel rail reading. I figure the cold start reading might be a bit lower than actual rail pressure due to the small diameter and length of the line, but the pressures I read were almost exactly what the F.S.M specified.