I'm with larson on this one, but anything is possible. You might want to verify that he has the title in hand before you touch the truck.
Whatever you do, make sure the engine's stone-cold before you try to light it off. If he's gotten the engine running and warmed up before you get there, go back another time. He could be masking a cold-start problem, which may be as simple as bad glow plugs but could also indicate low compression.
For that matter, while running 12 volts to the fuel shut-off solenoid on the injector pump will bypass the key switch, you'll also want to activate the glow plug system...on an '86, that should be as simple as running 12 volts to the small wire on the glow plug relay (should have a purple wire on there at the moment); just keep 12 volts on for 8 seconds, then off for 8 seconds, and cycle it a few times like that before trying to turn over the engine. DO NOT let the plugs cycle for longer than 7 or 8 seconds without an 8 second cooling off time in between, otherwise you risk burning out the lugs and having swelled tips.
Hope this helps some...good luck!