Actually 52 5/8 is housing flange to housing flange, that number stays the same regardless of what axles you use.
Wheel mounting surface to wheel mounting surface (“drum to drum”) the SBP axles are 57 1/8”, if it’s been converted to BBP then ~57 13/16”.
If you need to check out an axle, most of the 8 3/4 dimensions are listed here. Both housing flange to flange and drum to drum measurements- An accurate 8 3/4" rear axle width list
I was led to believe the early axles had the 741 and at some point after the late 60s switched entirely to the 489. What exactly is the difference between the two?
The 741’s were around until ‘72 in the A-bodies at least. My ‘71 Dart has one and it was the original.
The 741, 742 and 489 have different pinion diameters. 741 is the smallest. The 742 is the next largest, then the 489. The “which is stronger” thing is more complicated though because the 489 has a tapered pinion.
