The easiest way to spot a TH-400 from the top or sides:
1- The tailshaft housing has 6 bolts attaching it to the main body.
2- There is a 1/4 inch spade type wire connector protruding from approximately 1-inch above the driver side rear corner of the transmission pan.
3- There is a vacuum modulator located on the passenger side front, straight outward, the modulator is located pretty much between the dipstick tube, the remote cooler fittings and the front pass. side corner of the pan.
This is the easiest way to explain without pictures.