What is the best trans fluid these days for an A-727

i have used syn fluids in all my cars for over 30 years and have never had a failure , except one 1998 explorer trans go at 250,00 km .First thing I do with my new cars is change all the fluids for syn fluids ,
So if I put CHY atf+4 it will be a good choice ? I believe in synthetics , just not sure on a 1970 transmission , but if you say it will not do damage , it's a go