Here's why:
* Bolt Pattern: The bolt pattern for the engine block where the bellhousing mounts is different between big block and small block Chevy engines.
* Transmission Mount Location: The location of the transmission mount on the bellhousing is also different.
* Overall Dimensions: The overall dimensions of the bellhousing are different, as the big block is physically larger than the small block.
Important Note: Even if you were to attempt to modify a BB bellhousing for a SB, it's not recommended. The modifications would likely weaken the bellhousing, putting the transmission and engine at risk of failure.
To correctly match your bellhousing, you'll need one specific to the type of engine and transmission you are using.
