I think the only diffrence is the size on the spring bolt. The 91-93's are bigger. You could fix that with a different bushing.
ON this site they have lifts for a 89 to 91 lift for the first gen diesel..Does it matter if i put it on my 92? its way cheaper! also because its a system.. its on this site
69-93 DODGE 1/2 TON 5" - 6" KITS @ NTW[/QUO
Try a local spring shop just tell them what you want as far as height and what you have they are usually cheaper than the kits you buy.