My opinion is to keep your truck low for better stability. Really, 4" springs on a 3rd gen with 37s work really well! Take a look at these pictures, this is CruzrDave's 1990 with 4" Betts (All Pro) springs, 5" shackles and 37" MTRs:

 

Hey mike thanks again..this is the perfect setup that I am looking for.. so this is the all pro 4" sas kit I am assuming. Ya the 5" just might be a little up there. I want great flex and stability. Thanks mike!!! Ill let u kno like I said wen I start.

 

It is our Marlin Crawler Trail Flex kit which uses the same springs as the All Pro kit. We don't make & sell the kit any more and refer all customers to All Pro for their excellent kit. You will not be disappointed with their 4" kit!

Also, regarding the rear suspension on Dave's truck pictured above, the rear fender line is lower than the front. It sits perfectly level and looks great!

Have fun with everything! It sounds like you are gonna build one sweeeeet ride!