Good call on the axle flange. I research more to verify that and yes you are correct (as I already assumed via your reputable knowledge)Click image for larger version.  Name: $_57.jpg  Views: 8  Size: 97.3 KB  ID: 2525

I see I am opening a can of worms here. My next question was going to be "how about stepping back one place to a 722.5 upgrade?' -but then I see even using the 3.45 diff from the W140 like you suggested would still put a 722.5 5sp box in the same overall 1-4 final gear range I already have...but with an overdrive (5th) that would be useless.

Thank you for your helpful input everyone. I would say at this point the OEM rebuilt swap is in rightful order. This is not my race car and is not economically a smart move at 3-4 times the cost of a simple OEM replacement.