If you are going with boost (turbo or blower) the 03-04 is, hands DOWN, no question, the way to go. Several advantages:
1) forged bottom end (crank, rods, pistons)
2) solid iron block that is good well past what you'd probably put in it
3) COMPRESSION RATIO*** is lower in the 03-04's...obviously if you're building a car for boost, lower compression ratios mean you can run the engine at higher boost, for more horsepower.
Bottom line: the 99, 01 Cobras, the GT's, the Mach1's, etc...all were built to be in the 300 hp range. Thus the internals were built with this in mind (and will ALL blow around 450+hp). They were built to be NA, all-motor cars...the compression ratios of all of them reflect this fact. They are higher to squeeze out better hp b/c the manufacturers didn't build them to take boost. The terminators were built to take boost from the factory: the comp. ration is lower to accomodate high boost levels, and the forged rotating assembly ensures stability and reliability for years at 700-800+ rwhp.
This really isn't a debate...if you're going for boost, the answer is the 03-04s. | 
