That's kind of confusing, i dont think the fuel feed to the carb is Teed to the return line but maybe I'm reading it wrong
Anyway, you cant monitor fuel pressure on the return line
I used to measure my fuel pressure a couple times a year directly off the regulator
You could tee into the fuel feed hose I'm sure but it gives you more potential for a high pressure fuel leak and that's scarry on a front mount
I would mount the gauge as close to the reg as possible if i were you
Oh, the return line has no hose inside the tank