Yeah, that's where I'm screwed with my TTB swap for my V8 Explorer... I found the cheapest axles I could and they were already removed... there is no kit, you're more likely to find a kit to put a D30 up there...
I plan on putting in a D44/D50 hybrid in my '00 Explorer probably next year, hopefully start on it this winter and start the parts acquisition process... I already have a D44 TTB, a D50 TTB and two 10.25's... I think I have under $200 in all 4, but all were acquired without measurements... I'll be rigging things up before hand, might just weld the beams together temporarily to get pivots figured out...