Maybe it has to do with the earlier bushing (through 1950) having a pin that holds it in place and the later (51-54) bushing just being a press fit. Do you see a side pin at the end of your torque-tube? The replacement "Okie" bushings are different, so the diameters are most likely different?

Patrick's is probably being careful about being sure what year torque-tube you have?

Jim Carter
Chevs of the 40s
Classic Parts