The Muncie 3-speed serial number is located on a boss above the filler plug. The Borg-Warner T-16, 3-speed serial number is located on a boss at the right rear corner of the transmission extension.
Serial numbers of 4-speed transmissions used in models prior to 1979 are located at one of the three following locations: left side cover flange; left side of the case to the rear of the cover; or the left side of the case below the side cover.
1979 and later transmission I.D. numbers are located on a flange at the right side top of the case.
See Figure 1
1978 and prior THM 350 serial numbers are located on the right side vertical face of the transmission oil pan.
1979 and later 3-speed automatic transmissions are coded either on the right side of the case above the front of the oil pan, or on the case above the left rear of the oil pan. The THM 400 and the THM 700-R4 4-speed automatic transmissions serial number is located on a tag attached to the transmission case, above the right rear corner of the oil pan.