There is a schraeder valve fitting on the right side of the facotry fuel rail on a stock 496 right at the rear of the white coolant bottle. Make your fuel pressure guage connection there for a testing location only. I would never recommend running a fuel line from a pressure fuel system to a boats guage location, TOO LONG, TOO DANGEROUS. As for a snding unit on the motor with wiring to an electrical fuel guage on the dash, to unreliable from a calibration standpoint. Why are you monitoring fuel pressure on your 496?
Ray At Raylar