Sorry for not giving full details. I am replacing the tank and installing an in-tank fuel pump to feed an EFI. The tank vent and the pump vent Y into a single vent line that is supposed to go to this valve.
Is your neck vented now? If so, I would leave this additional vent out and cap the vents on the tank and th pump. I have a 70 with a vented neck, and was told by tanks, inc that should be fine.