[Gromit]

Maybe I am too cautious, but once that sender is removed at the upper tank, any tiny static electricity spark (even a spark not visible to the eye); could potentially ignite that air/fuel mixture in the upper tank. I believe this would occur faster than any feasible human reaction time.

I've removed those senders myself; but I think of it as one of the sketchier things I have done on these trucks.. The worst thing in my opinion would be the initial blast would take out your eyesight, and it might make it more difficult to respond or know what to do when you cannot see; and if you are drenched in flaming gasoline from the burst tank.

But anyway to respond to your actual question; the mechanical pumps are only $20 or $25; so it would be easy to just try out the spare.

It is also pretty easy to put a hose pinch off clamp on the lower hose by the frame rail and disconnect the rubber connector there and at the fuel pump and blow out the steel line (and make sure it isn't crimped (for example by someone trying to force the trans support back too far) between the tank and the pump).

I do remember the first time I blew out that line I didn't notice that the fuel pump supply pointed back toward me under the truck and when I hit it with compressed air it blew all the contents of the line back all over me.. I only did that once.. (I'm not claiming to be a genius here, just a regular guy with the bulk of my brain cells devoted to thinking about a woman)..

The previous owner of my truck did fry the pump diaphragm and fuel did get past it and enter the crankcase to mix with the oil.. That is a pretty fatal design flaw IMO.. a good argument for a separate electric fuel pump unless there is a mechanical pump that is sealed off from the crankcase..