Go to the junk yard and find a 5.0 Explorer, 97 and up I think, and get the heads. GT40Ps are good heads and should give you a few ponies and noticeable performance gains. If your car is injected you could probably do well with the Explorer's intake as well. I got my set of heads for less than $70 complete with rods and everything. I would also say gears.
now go score an Explorer itnake from a 96 if you need to stay emissions compliant - or - port your stock lower intake to make your stock HO intake flow ~190cfm to match your GT40 heads and it will have great torque! Instructions on porting the lower are on my website in the tech section.