NB Fuel Return Question
 

I have a MSM, and I was doing my Walbro 255 the other day and I see we actually have a return line. Unless I'm not understanding my fuel pressure regulator correctly.

Anyway, what stop us from just removing the intake FPR, and plumbing one right after the fuel rail with the existing line?

Everything is stopping you. You have neither a return line nor a FPR at the front of your car.

The line you are incorrectly calling a return line is for vapor purge. The device at the frame rail is a fuel damper.

There is a return line on NB miatas, but it happens to be immediately after the fuel filter, and nowhere near the engine bay, where you seem to be looking. That's all fuel dampener stuff.