Well, if you really put your heart into it you could have a helluva vehicle. It's not impossible to build your own wire harness - trust me if a boob like me can build a weapons system harness for an F-16 in the field (well, as afield as the AF gets anyhow) then I know you can build an efi harness for your rig. Sit down with the wiring diagram, pull everything from the truck (engine, tranny, exhaust) and go from there.

If I were going to rebuild the whole thing I'd start by finding all the connectors - determining what you need to 'plug right in'. If necessary diag out all the connectors you need and mate up connections for them to your new harness. Don't just crimp them together, solder the things then heat-shrink over it. Try to find another 86 4x4 so you can note where wiring has spiral-wrap, heat shielding and the like.

If you really put your mind to it you should be able to nearly duplicate the quality of the old harness.

Rebuilt tranny, new/rebuilt motor, paint job, 4 new tires... rebuild the axles, replace all the U and ball joints...

It'd get spendy but when you were done it'd run like a new rig. If you also did the interior it'd also FEEL like a new rig.