* Engine Mounts: The Pontiac 400 and the Oldsmobile 307 have completely different engine mounts. You'll need custom motor mounts fabricated, likely requiring welding and significant modification to the Cutlass's frame or subframe.
* Transmission: The transmission compatibility depends on what transmission you're using with the 400. If it's not the same as the original 307's, you'll need to address the transmission crossmember, driveshaft length, and potentially the bellhousing.
* Exhaust System: The exhaust manifolds or headers for the 400 will not fit the Cutlass's frame. A completely custom exhaust system will need to be fabricated.
* Wiring Harness: The wiring harness for the 400 will be different. You'll likely need to modify or completely replace the existing harness, potentially requiring a significant amount of electrical knowledge and troubleshooting.
* Cooling System: The 400's cooling requirements might differ from the 307's. You may need a different radiator, water pump, hoses, and possibly even a different cooling fan setup.
* Steering and Suspension: The added weight and different dimensions of the 400 might necessitate adjustments to the steering components and possibly even the front suspension to prevent interference and maintain proper alignment.
* Fuel System: The fuel system might need modifications to accommodate the 400's fuel requirements.
* Computer Controls: The 400 is likely to require a different computer control system than the 307, which will further complicate the wiring and potentially require aftermarket components.
In short: This isn't a weekend project. Unless you have extensive experience with engine swaps, fabrication, and automotive electrical systems, it's strongly recommended you seek professional help from a skilled mechanic specializing in engine swaps and custom fabrication. Expect this to be a very expensive and time-consuming project.
