zf6 loocked up at 65mph...

[msdg137]

I was just starting out on a 4 hour round trip to pick up a motor when my truck started stumbling and bumping as if it were misfiring, I rechecked the guages I had just checked minutes ago, all reading normal... The within seconds it got worse before hearing a loud crash and what sounded like a rod going through the block. I pushed in the clutch and turned off the motor ... Big Mistake! It was the tranny locking up that was rapidly slowing the motor down making it feel like a misfire. I pullled the truck out of gear and rode out the on and off tranny lockups making my way to the shoulder.

The truck seems to have all forward gears but rattles like hell as if its eating something, reverse seems to be binding. I pop out of 3rd as well... Where should I start?
I found a local 6speed out of an 04 4x4 6 liter f450 rolling chassis for $700...
But Im a 99 f350 7.3 and only 2wd...
Can I swap the tail shaft on the tranny and run it?
Im bright enough on a good day to rebuild it if the price is right...