According to the Mustang Production Guide, the D-code 289 4V was the 2nd most common of the four available engines in the '64.5 models. The F-code 260 2V V8 was 47% of production, the D-code 4V V8 was 35% of production, the U-code inline 6 was 17% of production, and the Hi-Po K-code 4V 289 V8...