I put a single disc parking brake on my Ford 9" --- bolts onto the yoke -- has a hand brake style lever - it's own disc (tiny) -- it's a PARKING BRAKE not an "emergency brake".
http://www.tsmmfg.com/Pinion_Mounted_Parking_Brakes.htm
Mark -- Good info on the residual valves not working. I didn't think they would because that's not really their job... but thought maybe it might help.
Gonzo -- Can I tell ya sumthin....
