On the "Crash Box" oil change info, see the snapshot from a 1942 Chevrolet Army Truck Manual (applies to your transmission) for what I've found to be the best description of a transmission oil change. The regular shop manuals basically just say drain and refill.
Here's an original Chevrolet
Crash Box 4 Speed Rebuild Filmstrip courtesy of fellow Bolter Brad Allen that you will surely find useful.
Others with more experience in the "Crash Box" will most likely come along and chime in soon.
