I have to read the fuel pressures on my 1979 450 sl. I have looked at a lot of kits online and they are pricey and I'm concerned about having the right thread size and style to fit the standard fittings on the FD and WUR. I was thinking of installing a gauge and shut off valve inline on the tube from the FD to the WUR and that way it would always be there for me to check any time. Anybody see a problem with that. Something that I'm not seeing????