Before you change springs I would look at your shocks. If you have gas shocks all around you may want to change to an
oil filled hydraulic. They will give a much better ride. If the ride height is ok then the springs are probably good. I've been using the Pro-Shocks front and rear and the ride is great. Both DV and I are dealers for Pro-Shock so if you want more info let either one of us know. I use the flaming river manual rack and it works well in the Cobra.
As far as engines I have built and sold many engines. We do have a dyno in-shop and can build anything at any hp you want. Our largest to date is 1100hp. I'm a little ways from you but trucks run everywhere and shipping isn't to expensive. DV has used my engines with great results. Let me know if I can help.
Don