Well, if I'm reading this right, you need to cap off the line that runs back to the tank; thats were all your pressure is going. Afterwards you should see about 7psi at the gauge. So, you'll have the line from the electric pumps in the trunk going to your carb(s) and the other line will be capped off and not used.
I would probably consider installing a mechanical pump just to make everything run as designed, but thats by no means necessary. If you don't have a fuel level gauge, then the reserve is a nice feature so you don't have to count the miles until empty.
