* Engine Compatibility: The 4.6L V8 itself is largely compatible. The mounting points are generally the same between the two platforms.
* Transmission Compatibility: The AODE transmission is also used in Thunderbirds of that era. However, there might be slight differences in the transmission mounts or even the length of the driveshaft required.
* Wiring Harness and Computer: This is the biggest potential hurdle. The engine and transmission computer (PCM) are calibrated differently for the Crown Vic and Thunderbird. You'll likely need to adapt the wiring harness or possibly even use a Thunderbird PCM. This is a significant undertaking and requires considerable electrical knowledge.
* Exhaust System: The exhaust system may not be directly interchangeable.
In short: While the core components *could* fit, you'll likely encounter issues with the wiring harness and potentially the exhaust and transmission mounts. You'll need to compare parts carefully and potentially fabricate some components to ensure everything lines up perfectly. A professional mechanic familiar with these cars would be invaluable. It's not a simple bolt-on swap.