My first question would be - why a Galaxy? Mustang pumps for 1966 are Falcon pumps and are 'similar' to full size Fords and Fairlanes. The differences are in the pulleys. The standard 'it will fit' line of some is based on what's at the auto parts store, which are usually sold without the pulley. If you have the correct engine mounting brackets, pulleys, belts, drag link, tie rod ends, ram, ram bracket and hoses, all used on 1966 Mustangs, it will work - otherwise you will have problems.