If you're looking for a high quality fuel pressure gauge, this is the one we recommend.  Being liquid filled, it prevents the needle from pulsating back and forth as the fuel pump cycles.  This gives a more accurate reading on the gauge.  The back of the gauge has 1/8" MPT (male pipe thread) fittings that screw into whatever adapter you choose to use in your fuel line.  Simply tee in in downstream of the regulator or fuel pump and before the carbs.  

TECH TIP: Always use a wrench to tighten this gauge into the fitting where installed.  If you turn it by hand by the dial, it will fail immediately. There is no warranty on this gauge for this very reason.  They are factory pre-tested and guaranteed to work.