There are natural differences between the 4- and 6-cylinder models. The 89 SWB/LWB will have a funny little set of mounts from the body to frame in the rear fenderwells. The biggest diff will be the engine/trans and things directly related, bolted to, and attached. The body, interior, etc. have nuance differences. The 89 SWB may have rear 3-point seat belts, some vertical bars inside the rear window, rear interior panels have a hole for the seat belt retractors, speaker covers are not the same but can be used. The 89 most likely has a rear wiper delay not found on the 87. The rear frame crossmember is difference to accommodate the larger tank and the bumper mounts are accordingly different.

I have not had a V6 SWB, but the interior dome light could be different. Comments about are based upon numerous LWB and 4-cyl SWB models I've parted out, or from wrecking yard forays. Buy the V6 and get larger front brakes, too!

Russell