See Figures 1 and 2
A transmission serial number is stamped on each transmission case or to a plate which is welded to the case. Location of the ID number will vary with the transmission manufacturer. With the Borg Warner T-5 transmission or New Venture Gear 1500/3500, locate the transmission ID number on the front right of the housing.
See Figure 3
The identification number for the 4L60-E is stamped on the right rear of the housing just above the pan rail.