Generally the same people who have used them in the past. Like me, for instance.

Okay, lets say I run 35 x 12.50. Would a 4" lift look and function right? All-pro front springs move the axle forward 1 1/2". After I beat the seam in the tire well down, I should have enough room, correct?

here is my wifes truck, no lift, 34 inch tires. I cut the fenders and the rear of the fender to the cab mount.
she loves the ride, and it don't flex to bad for stock shocks. stock springs, stock steering..

Can someone clear this up for me please. I've noticed that instead of getting taller springs some get longer shackles and a drop front hanger. Why would you want to do this over just getting taller springs. Are flatter springs better for ride quality or flexibilty.
Thanks

The drop hanger design was originally for SASing IFS trucks and you have issues to work around like a lower front IFS frame and steering box that need clearance and a dropped hanger "can" offer better clearance. The other reason is that longer shackles are typically used for better articulation and you need to match the front and rear so that the front diff pinion angle is at least close to stock. And finally, it's easier for a layman to weld on a single front hanger, so they were designed to be beefy and one piece and that made some lower the hanger a bit.

Everyone is offering great advise here. Definately stay away from a bodylift/spring lift combination. Maybe one or the other.

I ran my SAS with 35s with 4" of lift and cut fenders and more room than I ever needed. Probably could have cleared 37s. Moving the axle forward a bit is an important factor.

Whatever you do, you don't want too much lift. And since you're lucky enough to have an '85 with the high arch frame, take advantage of it and run as low lift as you can for more trail stability. Unfortunately, SAS trucks like mine pretty much can't go any lower than about 4" of suspension lift, because of the frame.

If you're gonna run 33s, I like the idea of trying to keep the lift close to 2-3". If 35s, absolutely no more than 4" is needed as I've proven.

All things being equal, a long flat spring will flex more than a highly arched spring. The more arch a spring has the stiffer it is. My front springs only give me about an inch of lift, if that. The rest (3") comes from the lowered front hanger and longer shackles:

http://www.4crawler.com/4x4/4R_suspension-III.shtml#Update-part3

try trail gear, great price and the parts are quality, i know a guy with this kit and 63'' chevy springs in the rear, he goes everwhere with his 36x13.50 iroks

http://www.trail-gear.com/classic.html

i like this kit because it includes the hub kit and the knuckle rebuild kit. just add an ifs box and your good.

NO lift.....37" tires.