Well, your gonna have to measure the inner diameter of the spindle to determine wether you have a 72 or 73 spindle.
The 72 uses a smaller diameter inner bearing, and a 73 uses a larger inner bearing.
The 73-76 A body spindles (brakes) are pretty much considered the ones to find and use, as they have the large bearing.
If you do have a 73 E body spindle, (or 74) those are a good one, as they are the same as the A body.
Confused yet? lol