The GM TH400 has a case length of 24-1/4", 13 bolts for holding the oil pan in position and is available in 3 different engine to transmission bolt patterns. Make sure you have selected the proper TH400 for your particular engine. The rear side of the transmission case will have a hex shaped bolt pattern that uses 6 bolts. There are several various lengths of output shafts that the transmission has been equipped with. The shaft that works with this adapter is the one that is 6.9" overall. The shaft when installed into the TH400 will stick out approximately 2.5".