You have to get a Mustang engine. The T-bird was discontinued in 1997, and that 4.6L engine is a pre-PI engine. Lack of HP & TQ.
Stick with an 01-04 engine. 99-00 have not as good heads and intake, and the timing cover and tensioner are different.
I don't have a good one right now, the one I have was hit low and needs some work. The heads an intake are all good, but I think you may have PMed me about that before.