Advise needed: Air Shocks

"changes in the Rear Suspension would likely notch it up a bit when launching.."

Working off of your words. Leaf spring suspensions are very simple in design. they simply suspend the vehicle's weight on an inverted arc. Nothin to it, right? Until you start wanting to hook up or make your launch better. Air shocks and even gas shocks make leaf spring suspensions sorta useless in terms of a launch. If you want a better launch with stock springs, add a pinion snubber. It will force the rear suspension to work for you and plant the tires. Air shocks do not allow the leaf springs to compress and will cause the rear tires to lift off the ground. That ain't real great for traction. Gas shocks can essentially do the same thing. The best thing to do (although not the most cost effective) if your springs are sagging is to replace them. I would go with the XHD springs from Mancini. They will work well and not be as harsh as the SS springs. Also, a nice regular heavy duty hydraulic shock in the rear will work best, regardless of all the hype and marketing you see and hear about fancy gas charged shocks. They are cheaper, too. I know all this is probably more than you wanted to do.....BUT you did say you want to make your launch better. You're not gonna do that with air shocks or gas shocks or add a leafs.