I dont know if this would work, but I got to thinking about somthing. the new 2005 Mustang GTs have a 4.6L with 3 valves per cylinder..... in theroy, you could replace the heads on your 2-valve blocks with the mustang heads for more power...

This would only work if they both use the same block I would think. Seems like a pretty good bang for the buck...

Just an idea for you 4.6L guys looking for more power. Dealership might even do the work for you...