[andy669]

Its going to depend on what drive gear you have. Chances are you are going to have a green (8 tooth) drive gear. If thats the case it will need to be changed to a yellow (7 tooth) or a black (6 tooth). If you use a 7 you will need a red (21 tooth) driven gear. If you go with the 6 you will need a yellow (18 tooth) driven gear.

All of these can be bought at any ford parts dealer. Heres the part numbers.

Drive Gears:
6 tooth Black - E3ZZ-B
7 tooth Yellow- E3ZZ-A
8 tooth Green - F0ZZ-A

Driven Gears:
(manual trans)
17 tooth White - C3DZ-C
18 tooth Yellow - C0DD-B
19 tooth Pink - C0DZ-B
20 tooth Black - C1DZ-A
21 tooth Red - C4OZ-A

Hope this helps
andy