I can say that Cubey bypassed his FSV today. He's now running on only the rear tank. I hope that he posts up the results soon.
It seems fine. One hose end might have been lightly seeping after 20 miles. Not a drip though. The clamp was a bit close to the hose barb end, so loosened it and I moved it slightly before tightening it back.
I double checked the Haynes Bronco/F series manual on which ports of the FSV were which vs which I used and it seems correct. It confirmed what I saw, the top two are front, lower two are rear.
After the 42 miles to where I am now, the rear tank gauge reading dropped about the right amount for that distance. I should have another 100 miles before I hit 1/4 tank. I will probably refuel a bit sooner to be safe but yeah.
Assuming the 22gal tank gets used to a
1/4 tank from 100% full, that's 16.5 gallons. At about 8.8mpg combined mpg, that's 145 miles. It gets a bit better highway only but that's a good rough estimate with some stop and go thrown in.
The front tank reading still shows about 1/4 tank when I flip the FSV switch, so it doesn't seem to have the return hooked up by mistake.