use a c-4 they are very strong cheap to build and much much lighter esp. when your trying to put it in (faster). you could build it yourself it only has two clutch pacs and two bands in it the c4 is much harder you can have your local tranny shop put the clutch seals and springs in it cheap conv are cheap to go to
http://www.transonline.com/ for how to.
you definetly want a double hump crossmember
from 86 up car. (for dual exuast). the rest will bolt in using 302 mustang parts. ive seen guys make 302 headers fit. but they do make customs svo sells them try jegs summit paw call theyre not always in the catalogs.
there is certain years of c-4 that are better but i dont quite remeber. think mid 70s and newer. or if you want to drive on highway aod would be good investment. good tranny if built right. not for begginer builder though.