If your going to go for coil spacers I would suggest new springs instead. Primarily my preference, but I believe they are a better choice than spacers, and less work to install. Even to fit 31's on a 91 will take a little work. I have 6+ inches of lift on my 90 and i'm only running 31's. I can tuck 33's with the proper backspacing. Check out Rough Country for a cheap 4" suspension lift for your truck. It runs less than 500 dollars, and for a suspension lift, its extremely reasonable. If you want to go on the cheaper side, you can run a 2" lift coil in the front with cam bushing for proper alignment. You won't be able to lift the front end much more than 2" without drop brackets and still get it aligned. If 31's are your goal, a 3" body lift should get you just enough lift for that. According to TRS
, 3" body lift is the minimum for 31's.