Ian -
Sounds like your are doing the LP pump and letting the Pollack valve do the switching, I like that and anything to get rid of an extra pump is good.
No sure if this is what you were saying, but after talking a bit with one of the pump manufactures about the pumps I have (SX Perf inlines), they commented that the return line should be -6 minimum and not restricted since the pump has a lot of volume and pressure. It would not really matter if the swirl pot was in the equation or not, ultimately the return will have to carrier the normal High pressure return. Another interesting idea was to pressurize the swirl pot, but came up with the same conclusion that it would just collect air and not work. The SX Performance pumps and other can be fed with a low pressure pump as the tech told me. Another issue that I thought might be a problem is if the HP pump is pushing back a lot of fuel into the pot, and the returns have restrictions it may have to have a check valve on output of the LP pump, might be over thinking, but that is a known problem I have
One question I never really thought about was what was the acceptable minimum size of tank that could be used. A gallon seems large, but don't really have a feel for what it might need.
The crash worthiness was also a concern and I'll likely make something out of rectangular or round heavy wall aluminum pipe vs. Sheet metal like ATL's and others (It's also easier to weld then the thin tanks).
The KISS principal would be to use just one tank and it would clean up lots of stuff, but as you know we have to add something to do and making it too easy would not be in the spirit of things
Sandy