Well ya started this in the interior section, but...
If your 89 has the small quad lamps, the one piece composite lamps from 90-up are bolt-in. You just remove the grille, and each headlight bracket has 4 bolts, when you have those off the 90-up lights bolt right into the same spot.
The connectors for the bulbs are different, though. You can splice 'em on, just be sure to solder them and use heat shrink tube. Crimping them or twisting/taping is not going to cut it; the headlights have a serious current draw and you don't want to depend on a crummy connection.
Or, you could replace the front lamp section of the harness from a 90-94 truck that came with the composite lamps. You can separate it at the firewall with a small amount of work; there's a screw in the middle of the block, remove that and pull the block apart, then with a little puzzle magic using a small screwdriver or pick, you can release the tabs that let you get just that section of harness loose from the assembly so you can work forward and get it loose from the core support, headlights, turn signals.
Richard