I have a Prime-Loc fuel filter replacement on my truck. I want to put a fuel pressure guage on the system so I can check the pressures. Prime-Loc has two ports to tap into. I'm guessing one is for pre-filter pressure and one is for post-filter pressure. I want to have a guage on both ports. I am looking for some generic guages. What kind of guages can I use and do I need an isolator? I have heard of using a needle valve but I can't find one with a standard NPT fitting.