The 351 Windsor is a larger engine than the original 289 cubic inch V8 that came in the 1966 Mustang. As a result, it will not fit in the engine bay without some modification. The most common modification is to install a larger radiator and a set of headers that are designed to fit the 351 Windsor engine.
In addition to the modifications to the engine bay, you will also need to make some changes to the transmission and driveshaft. The 351 Windsor engine uses a different transmission than the original 289 cubic inch V8. As a result, you will need to install a transmission that is compatible with the 351 Windsor engine. You will also need to install a driveshaft that is long enough to fit the 351 Windsor engine and transmission.
Overall, installing a 351 Windsor engine in a 1966 Mustang is a relatively straightforward process. However, it is important to note that it will require some modifications to the car. If you are not comfortable making these modifications yourself, you should consult with a professional.
