I would go with where you got the FI from. Most dual tank setups are found in 3/4 and 1 ton trucks, anything with TBI and dual tanks should work...so 87 to 94 Chevy or whenever they stopped using TBI (I can't recall the actual cutoff year).
I know most companies used TBI for a long time to but it'd be a pain to see if they used the same PSI so I'd try to stick with Chevy's and GMC's unless you just can't find any.
Here's a universal one that works up to 40psi...it looks like most any will work although I just ran across a couple that specifically state less than 8psi. Make sure you get one with the fuel return lines too.
eBay Motors: FUEL TANK VALVE SELECTOR SWITCH GAS UNIVERSAL 6 POR FV5 (item 200217505763 end time Feb-13-09 07:10:27 PST)