Here's why:
* Different Bolt Patterns: The big-block Chevy engine uses a different bellhousing bolt pattern than the transmission used in a 1966 Cadillac DeVille (likely a Turbo-Hydramatic 400 or similar GM automatic). This means the engine and transmission won't directly bolt together.
* Transmission Size and Type: Even if you could somehow adapt the bolt pattern, the physical size and dimensions of the Chevy big-block and its associated bellhousing are likely incompatible with the Cadillac's transmission and surrounding chassis components. The DeVille's transmission is designed for a smaller engine.
* Output Shaft: The output shaft of the Cadillac transmission is probably not compatible with the Chevy big-block's requirements.
To make this work, you would need an adapter plate (a highly customized part), potentially a new transmission, and significant modifications to the engine bay and transmission tunnel. It's a major undertaking, far beyond a simple swap. The cost and effort involved would likely far outweigh the benefits.
