Ya, that's another option. I doubt it'd be CHEAPER or LIGHTER than a
reversing pump, but if I can't find a reversing pump then such a valve
may be my ONLY option. So OK, I'll bite:

Where can I get a quality valve that supports swapping of inputs and
outputs, and will handle gasoline?

I actually had this drawn up long ago with a standard 4-way valve (such
as used with fuel-injection), a pair of one-way check valves, and lots
of interconnects. It seemed to be overly complicated. I can't find
that sketch now, tho' I'm sure I can recreate it with a little thought.

If there's a purpose-made valve for this, that would be GREAT.

Thanks,
Greg