Technical Inline Fuel Pressure Gauge

OK. You used 5/16" tubing. The common female branch tee for 5/16" tubing has a 1/8" pipe port on the side so it's a direct fit to the common fuel pressure gauges. Good luck should you decide to do it. You might even find a short piece of tubing at NAPA that you could add in as you seem to want avoid any cutting and flare work.