Assuming that connections will be the weakest spot in any system, and
that there actually is a pump that blocks flow when there's no power
applied (I haven't tried to determine if there is),  I would argue that
the pump IS the cutoff valve,

This is another one of those questions I've never seen a good answer for, so out to the garage I just went.  I grabbed one of the Walbro in-tank pumps, and tried with all my might to blow through it, and could not.   With the exception of my cheeks, I feel better now.  My RV-3 has no fuel shutoff valves. Rusty (forgot what I was going to put here)