3.8L and the 4.2L are the same block. Big difference is the crank. I'm not sure if the pistons are different or not. I'll hae to check that out next time I'm at work at Advance.
Platnium, all your accesories are the same between the 4.2 and the 3.8.
Have you thought of using 2000 Mustang upper and lower intakes gasket matched to each other and to the heads? It should fit under the stock hood without cutting it.
The Parts Bin Special is DEAD! It is being parted out.