1998 GT 4.6L

There's really not much to it. Take the stock block, fortify it with better rods and pistons from any of the major engine builders (MMR, Modular Depot, Modular Performance, CHP, etc), top it with a set of PI heads/Cams/Intake and you're good to go. A lot of guys are even running 150-shot on the stock bottom end with success....which when you add it to the 260hp the stock PI engine is pumping out, it brings you right to your 410hp goal.

As enticing as the 429 Boss idea sounds, judging by your post, it sounds waaaay over your head, not to mention will be far more expensive to do it properly. Stick with what works and keep your 4.6L and EFI. Your car is already set up to accept the mod motor and you still get to keep the great daily driver characteristics (good gas mileage, cleaner emissions, lower front end weight, cheap and plentiful parts replacement, etc).

No need to kill a mosquito with a sledge hammer when a flyswatter will do the job just as easily.