Mike..you are right..he SHOULD have an 8 1/4 being a V8..the one I parted out did not and was a 7 1/4 though it was a V8 also..the following is from ALLPAR....applicable to all M bodied cars..
Available transmissions included the A230 3 speed (Slant Six only), the A833 4 speed overdrive (Slant Six and 318-2 only), and the A904 and A998/999 Torqueflite 3 speed automatics. These were coupled with either the Chrysler 7 1/4 inch rear axle (for Slant Six coupe and sedan, non-towing applications) or the Chrysler 8 1/4 axle for the wagon, heavy duty, and V8 versions. Axles were available in 2.45, 2.76, 2.94, and 3.23 to 1 ratios, depending upon transmission and engine. Sure-Grip limited slip axles were optional. Torqueflites got a lockup torque converter in 1978 for non-heavy duty engines. Police Package Diplomats with the 360 V8 were equipped with the virtually indestructible 727 transmission.