I am in the same boat, here is what I think. I have a 97 Grand Marquis 4.6l 2 valve with the pi intake added after the intake cracked that's good for 20hp. I plan on adding the dual exhausts, 5.4l throttle body and intake and zip tube from the newer cars then send out my computer to get tuned before driving it, for those mods, but first I will do the rear end gears I have 2.73 gearing and no posi so first mod will be getting a 4.11 setup with posi, thats going to make the most difference in performance. I figure about 800.00 to get the Ford track lock setup new wheel bearings, seals, new rearend cover, gaskets, labour etc.. I don't mind sending my computer to the States I had to do that for my lighting control module already.