So I've also been researching solenoid-actuated valves, and have put in
some inquiries to several of the manufacturers as to their suitability
for gasoline. I can obviously do it with a set of four 2-way solenoid
valves, or with a pair of 3-way valves and a 2-way.

IMHO, a setup like you describe has too many possible points of failure.
Better off with the mechanical valve, for reliability.
--
Jim in NC