Here's why:
* Transmission Control: The 460E is electronically controlled. A carbureted 350 lacks the electronic components (like a computer and sensors) necessary to communicate with and control the 460E's shifting. You'll need to either replace the 460E with a mechanically controlled transmission (like a TH400 or a properly adapted C6) or add a completely separate electronic control system for the transmission, which is a complex and expensive undertaking.
* Bellhousing: The bellhousing bolt pattern on a 350 small block is different from that of a 460 big block. You'll need a 350 bellhousing to mate the engine to the transmission. Even then, adapting it to the 460E might not be feasible without custom fabrication.
* Torque Converter: The torque converter used for a 460 is significantly different from one used with a 350. You will need a converter appropriate for a 350.
* Mounts: The engine mounts will need to be changed to accommodate the smaller 350.
In short, while it's *possible* with extensive modifications, it's not a practical or cost-effective swap. Replacing the 460E with a more compatible transmission is the far more sensible route. Using a C6 would likely be the easiest mechanically-controlled automatic to adapt, however you will still need a custom mechanical linkage for the throttle.
