* Engine Mounts: The 3.8L and 5.0L engines have different engine mount locations. You'll need engine mounts specifically designed for a 5.0L in a 98 Mustang chassis, which may require custom fabrication or aftermarket solutions.
* Transmission: The transmission compatibility depends on the 5.0L you're using. A 5.0L might use a different transmission than the 3.8L (likely an automatic vs. manual, or different automatic transmissions). You'll need to ensure the transmission is compatible with both the engine and the existing drivetrain. This often involves replacing the transmission, driveshaft, and possibly the rear differential.
* Wiring Harness and Computer: The 3.8L and 5.0L use different wiring harnesses and engine control modules (ECMs). You'll need the 5.0L's harness and ECM, and potentially a significant amount of wiring modification to integrate it into the 98 Mustang's existing electrical system. This is a complex task and often requires professional help.
* Exhaust System: The exhaust system for a 5.0L will be different than the 3.8L's system. You'll likely need a new exhaust system or significant modification to the existing one.
* Cooling System: Radiator, hoses, and potentially the water pump may need to be changed or adapted to accommodate the larger 5.0L engine.
* Brakes: The 5.0L engine is significantly more powerful. You may want to upgrade your braking system to handle the increased performance.
In short: While it's doable, it's a major undertaking that requires mechanical expertise and significant time and resources. It's not a straightforward swap. Unless you have substantial experience in automotive mechanics, it's best to have this work done by a professional mechanic. Researching specific year models of both the 3.8L and the 5.0L you are considering is crucial, as the specifics can vary from year to year.
