Will modern type F Transmission Fluid damage 65 Mustang auto transmission Transmission previously filled with original gold fluid?

Answer 1

Personally I have never seen tranny fluid in Fords that is any other colour than red and my hobby experience goes back to the 1955 Ford-O-Matic which is the forerunner to the FMX.  But to answer your question type F is the same fluid whether it was manufactured two months ago or two decades ago. Ford still carries this fluid as it was used in several of their products in the late '90's in the steering. Plus other companies have used it. It is also used in heavy equipment as a hydraulic fluid.