October 1, 1970 to be exact. Some interesting reading.
Courtesy of Kirk Evans, here is:
Ford-Pantera
(DeTomaso/Cobra)
ZF 5DS 25/1 or /2 Transaxle Requirements
Report on Finalized Program Details
Status Date: October 1, 1970
http://www.spacecitypanteras.com/Technical/ZF%20Transaxle%20Requirements.pdf