On my 86 crew cab I have some 4" procomp springs up front that came off my blazer from a very long time ago. I was a little worried about the heavy ass crew cab destroying a set of springs but I already had a set of springs and why buy new springs right? Those springs rode really rough on my blazer but on the crew cab they are pretty nice. Rides kind of rough, but its a truck dammit. For the rear I used a 2 inch block because I wanted to maintain the load carrying capacity. It leveled my truck out perfectly. I was thinking about doing a shackle flip in the rear with air bags so that way they would ride nice and I could pump them up for some load carrying capacity. But I really didnt want to screw too much with what the factory already had back there. Theres one thing I learned from jacking with my blazer,,, its the same thing my dad told me..."manufacturers spend millions of dollars on engineering a vehicle for a specific purpose when you go and buy some hundred dollar part to through on there and jack it up." And when it comes to doing what the crew cabs do best (carrying weight) theres little need to F with what the factory already had figured out. If you still want to be able to tow, haul and be reliable dont go too extreme with the lift and modifications. Probably a 4 inch lift would be as high as I would want to go with 35's. Although I have a 4" and 37's, my 37's have a huge load capacity per tire. They are good just the way it came,,, although,,, like many of you Im sure would agree, it can always look cooler.
). In the rear I used a 4.5" block to retain the original spring capacity, the truck sits level now (as opposed to nose down). 
