66 Hertz clone from South Africa

Hi

I am a new subscriber writing from Durban,South Africa.I previously had a 1965 Mustang coupe which I recently sold to purchase a 1966 350 GT Hertz clone - it was a standard fastback that has been rebuilt as a Hertz clone.

Which brings me to my question.The car was a manual with 3.89 diff and 715 4 port Holley carb.I have converted it to an auto witha rebuilt C4 box - can anyone tell me what I should reduce the diff ratio to (it revs too high) and what the original carb was (600 ?) ?

regards
charles