I am working on a project to put together a guide that shows all the different transmission crossmembers for Mustangs from 64 to 73. Since I am not an expert with the early cars I needed some help with the early crossmembers and photos. It looks like there was two different crossmembers used up into the 1966 model year for the different engine/transmission options:
C5ZZ-6A023-A
C6ZZ-6A023-A
If anyone has photos of either version let me know, or can talk about the differences...