Carefully measured the backing plate flange on the AAM axle and here is the result.
Flange drawing PICTURE If made with the 3-3/8" ID as drawn it would fit on a 14 bolt axle tube to be welded in place.
I can't find any logic or reasoning in the pattern beyond the 5" spacing on the wide holes. Doesn't fall into a bolt circle, or a nice angle between holes, and as you can see not clean x and y distances from center. Converted to metric the numbers aren't round/clean either. It is what it is...
Before right now I could not find this info anywhere at all on the internet.
Grigg
