I'd suggest modding the fuel system to become a return type.
The returnless pump/FPR in your fuel tank is rated at almost twice the pressure the '96 Expo EFI system expects.
Factor in you'll loose the reduction in fuel pressure under high vacuum conditions and I think your '96 EFI is going to be in trouble.
Perhaps dropping down in injector size might get things close enough.
There's already a fuel return at the back of the '99 Ranger/B2500 fuel filter so simply removing the FPR in the tank and then piping the fuel return from the Expo fuel rail to the return line is a pretty simple solution.
You'll want to be careful with the speed signal. The ABS handles the signal using the ABS sensor at the rear axle. The Expo uses a gear driving VSS at the back of the transmission.
Both systems generate exactly the same signal, so if the two systems get tied together, you'll get a double reading at the speedo and internal to the PCM.
You could simply leave the speed signal wire open between the B2500 and Expo harness. That way, the PCM see's the transmission VSS signal, the B2500 see's the ABS's signal.
Alternatively, leave the VSS unplugged from the Expo harness, marry the Expo and B2500 speed signal wires and let the B2500 run the show.
Gotta say, since your B2500 does not have PATS of any kind, the non-PATS '96 Expo is a great option. Yea, a '99 Expo would have been easier with the fuel system and nearly plug and play with the wiring, but you'd have had to add PATS to your truck, or tuned it out of the PCM.
Either way, some mods were going to have to be made, and since the fuel system is not that big a deal, I'd say you're in a great position.
My own '02 is '96 powered so I did not have to muck around with PATS but did have to adapt the fuel system into a return type.