Will a 03 mach 1 motor fit into 96 mustang GT?

No, a 2003 Mach 1's 4.6L 3-valve motor will *not* fit directly into a 1996 Mustang GT without significant modifications. The 1996 GT uses a 4.6L 2-valve motor, and while the engine bay is generally similar, there are key differences:

* Engine Block and Accessories: The 3-valve engine is physically different in size and the location of many components (alternator, power steering pump, etc.). These won't line up with the 1996 Mustang's mounting points and accessories.

* Wiring Harness and Computer: The 3-valve engine requires a completely different wiring harness and PCM (Powertrain Control Module) that's not compatible with the 1996 system.

* Exhaust System: The exhaust manifolds and routing are different.

* Transmission: While it *might* be possible to adapt the transmission, it would likely require custom work.

While some enthusiasts undertake massive engine swaps, this would be a very complex and expensive project, requiring significant fabrication, custom parts, and a deep understanding of automotive mechanics and electronics. It's far from a simple bolt-in swap.