i KNOW that the chevy 1500's from the mid to late 90's? had torsion bars on them... you might be able to adapt 1/2 ton suspension to be on it, not so much for the spring rate, but for the durability, i would think 1/2 ton running gear on a small truck would be stronger than the stock stuff... but i don't know...
sawzall for sure, you said you are putting new leafs in, so i don't know if you will need the extra lift of a bl... and if you don't care how it looks, hack them right up!
you say racing, so i assume you mean fast speed, in which case i wouldn't do the longer shackles, they add flex and a little height... they kinda make your springs softer, because of leverage... but not really... and with speed i wouldn't think you would want extra flex... the 56" springs should give you enough for what i think you are doing...
essentially, with the shackles, leaf spring fully "compressed" is the same position, regardless of shackle length, but the truck sits higher when the spring is bent...
as for your cv's they aren't the greatest, but they are ok... i'm not sure what you mean by center sections though...
if you are all on dirt/gravel/what ever, welding the front diff might be an option too... but i don't know if it would help your situation...
because you said there's lots of contact, an exo-cage might not be a bad idea for a little armor... not sure if it's allowed within the rules though
i would also take out the rear windows to save on weight