Darrin,
You don't have to make this that complicated. Dimi's arrangement is similar to mine. I have just one low pump and one high. You have several problems with the tanks we have .
FLAPPER VALVE
The first is to get the fuel to stay around the pickup. You do that by adding a flapper valve or sump arrangement around the pickup.
When you go down hill or stop, the fuel will slosh forward and the pump will suck air. The LP is forgiving and it won't damage it unless it is constant. To augment that the return to the tank should be to this area as well. Thus making fuel available when those events occur.
BAFFLES
Baffles in the tank would help as well. Hope your tanks has them cause to add them is when the tanks are built. The flapper valve can be added by making an access cover above the pickup area. This cover can hold the fittings for the pickup , vent lines and fuel level gauge(cenntroid works best). The fuel level sender has to be outside of this arrangement. Otherwise it will show full tank all the time until all the fuel is gone!!
FUEL PICKUP
There is an argument as to where to have the pickup area. Some say at the rear of the tank. Some say in the middle. It doesn't matter as long as you lay out your lines and flapper valve arrangement correctly. The only difference is that if you put your pickup in the middle, you need two flappers, one on either side of the pickup to catch the sloshing to and fro. The vent lines still have to be at both ends of the tank(more about that later), and the return in the pickup area. .
FUEL LINES
First off the pickup needs to be a sock covered line to keep trash from getting into the line. This flows through a regular fuel filter to the LP pump. This then flows to the swirl pot which gravity flows to the HP pump. This line continues to a 75-100 micron filter on its way to the carb or FI. If carb you may or may not want a return line to the swirl pot. If FI you do. From the swirl pot the overflow line from the top should go to
only the tank where the pickup is located, and placed inside the flapper valve arrangement. This keeps fuel at the pickup during stopping or going down a short hill. Some will say to have a pickup in the front and rear, but I don't plan to be climbing mountains with mine. and one or the other will be sucking air almost all the time. If you park on an incline you may experience some trouble getting cranked, but there should be fuel in the swirl pot.
This was one of the early drawings. It has the return to the tank with no pump. This arrangement will over fill that tank and it will cause fuel leaks at the most inopportune moments. If it were an air tight arrangement then it probably wouldn't
Your next problem will be getting fuel from the other tank.. The tank that has no pickup will have a cross over line to the one with the pickup. It doesn't have to be big. A 3/8 or so line is fine. As the fuel in the primary tank drops the other tank acts as a giant reserve tank. These takeoffs are at the bottom of the tanks somewhere near the middle. Keep it low and level, not over any upper frame rails. I have a ribbed bottom so the line fits easily in the ribs and is protected.
If you are building a track car you may want a larger line. There should be a check valve in line here to keep fuel from sloshing back to that tank.. Routing this line will require some thought.
VENT LINES
You will need to run lines from the front and the rear. Here's why. With a full or nearly full tank there will be an air bubble at one end or the other. As the fuel temp rises from any heat source(sun or returning fuel) it will expand and if there isn't a vent it will buildup pressure. Opening a fuel cap would not be fun. There has to be one on both ends and they should be linked
with a rollover valve in place beyond the link. I have one that requires about 2cm of H2O pressure to exceed on back flow, so that air can get into the tank as its level falls.
I believe Demon Tweeks carries them. Where you put your exit is your option. I have mine at the fuel fill.
Sorry this was so long winded. Just a lot of material to caver. Hopes this covers your questions. PM me if this isn't clear.
Bill