I have had good luck with both of my valves in the engine bay, near the IP. Less hose between valve and IP means quicker change over.
I have 2 electric fuel pumps in the trunk, Converted the OEM tank to be heated, and run a 7 gal. fuel tank for diesel.
I cut a hole in the floor of the trunk near the tank so it was behind the pannels and could not be seen. Ran out of the hole, under the car, up over the crossmember near the steering box and up to the 3 port valve.
I was unshure too, so I just started building my HOH and seeing where it would route too easily and went from there. I think all of the home made ones are a little differant.

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83 300SD Dark Silver Dark brown inside