Something like this should work.
https://smile.amazon.com/Milson-Pressure-Gauge-Bottom-Accuracy/dp/B072PXNCX9/ref=sr_1_13?ie=UTF8&qid=1530683882&sr=8-13&keywords=pressure+gauge+1%2F4+npt

Doug


'89 Raider, 3 liter, 5 speed