* Engine Mounts: While the overall engine bay dimensions might be similar, the engine mount locations likely differ between a 1963 and 1968 Pontiac. You'll almost certainly need to fabricate or adapt motor mounts.
* Transmission: The transmission (automatic or manual) from the 1968 400 will likely require new or adapted mounts as well. The bellhousing bolt pattern might be different, necessitating an adapter or a different bellhousing.
* Exhaust System: The exhaust manifolds and pipes will not be compatible and will need to be replaced or custom-made.
* Steering: Depending on the specific transmission and accessories, the steering linkage might need adjustment or replacement due to potential interference.
* Wiring Harness: The wiring harness for the 1968 engine and transmission will be different. You'll need to either adapt the existing harness or create a new one.
* Radiator: The 1968 400 might require a different radiator, especially if it's a higher-performance version.
* Cooling System: Hoses and other cooling components likely won't be compatible.
In short, while the physical space *might* accommodate the swap, it's a significant undertaking requiring mechanical expertise and likely custom fabrication. It's not a straightforward bolt-on swap. You'll need detailed measurements and likely some trial and error to make it work correctly. Expect to spend considerable time and money on this conversion.
