If its an A body trans and has a slip yoke tail shaft, it should have a 2.66 first gear. 1966 till 1970 A bodies have 2.66 first gears and are wide ratio trans, 71 to 74 have 2.47 first gears which are the close ratio trans in the A bodies. The trans ratio you need is the 3.09 first gear which came in the 64 and 65 A body cars with slant 6 and 273 with the flange on the tail shaft, also made the 3.09 first in 73 and 74 only in the 318 Dart Sport and Duster with the 2.73 axle ratio. The overdrive trans from 1975 to 1980 use the 3.09 first gear too.
