rear shock help

[Ont67shortbox]

I am in the process of installing a 9 inch in my 67 shortbox.I went with the Jeep Wrangler springs for an approx 4 inch drop.I have the adjustable panhard bar for centering.What I would like is a single adjustable shock for drag racing to help with the launch.I have looked at several but not sure what part number or length i need.I had 6 inch drop springs and nitro drop shocks( 18 inches extended) but it wasn't working all that well.My 60 foots were around 1.72-1.78.I think I need a stiffer shock . Anyone run them and can give me a bit of help, Thanks Brian