* Motor Mounts: The engine mounts are completely different. You'll need to fabricate new motor mounts or use aftermarket ones designed for this swap.
* Transmission: The transmission and bellhousing are incompatible. You'll need a transmission that's compatible with the 5.0L, and likely a new bellhousing. This includes the driveshaft needing modification or replacement.
* Wiring Harness: The wiring harness for the 1990 5.0L is different from the 1996 3.8L. You'll likely need to adapt the wiring harness, or use a custom harness. This is a complex undertaking.
* Exhaust System: The exhaust system won't fit. You'll need a custom exhaust system.
* Cooling System: You may need to modify or replace the radiator and other cooling components.
* Computer/ECU: The 1990 5.0L uses a different computer system than the 1996 3.8L. You'll need the correct computer for the 1990 5.0L, and potentially a mass air flow sensor and other sensors to make it work properly. Wiring this will be complex.
* Brakes and Suspension: While not strictly engine-related, the increased power of the 5.0L might necessitate upgrades to the brakes and suspension for safety.
In short, while it's *possible*, it's a substantial project requiring significant mechanical knowledge, fabrication skills, and likely a considerable investment in parts and time. It's much more involved than just dropping in an engine. Many people consider this a difficult project, even for experienced mechanics.
