I don't qhite undestand why they "can't make" the new shafts. If they truly are making them, the diameter shouldn't matter, as they would be machining them to size. Doesn't sound like that outfit is much of a custom fab shop.
On a side note, I did a little bit of searching on a few sites, none of them mentioned any difference in bearing from Posi to open on that differential, exept for a "Open differential only" mention on the wheel bearing on Autozones site.
