We did a temp setup one time where we just hooked a hose to the filter drain pipe and clamped a gauge to it then opened the filter drain, quick and dirty but it worked, I was surprised the drain hose didn’t blow off the valve. Tapping the filter lid is a neat idea but those filter lids cost $$ to replace. I like plumbing the gauge into the head so I can see the pressure as close to the injectors as I can, in case something in-between is stopped up.