There is an Autometer gauge that REPLACES the schrader valve. It's around $190 and you can run it into the car. It has a sending unit and you just run the wires. If you are looking for a mechanical one that will sit in your engine bay I can't really help you, I don't know anything about those.
i have an auto meter electrical one in the car in an a pillar pod and the sending unit is where the shrader would be and i have a mechanical 1 1/2 inch mechanical auto meter plumbed into the fuel pressure regulator. my tuner said he found the electrical one more accurate, he said the mechanical one was reading a little higher and he said he's seen them go bad on supercharged cars using the fmu from pegging under boost. strange, could i dont use the fmu on my car.