dmc Hang on, the part that bolts to the drive shaft.
Ayup.... The output flange, which attaches to the propeller shaft, is held onto the transmission output shaft by a huge bolt. When you undo the bolt, the output flange slides off the back of the transmission, showing the splined output shaft undernealth. Anyway, you need to undo that bolt in order to remove the drive flange, so then you can slide the rear housing off of the back of the transmission.
Here's the back of the trans - the bolt I'm talking about would screw into the splined shaft from the left-side of photo to retain the drive flange. The splined shaft seen below would normally have the drive flange over it.