Not hard, I'd imagine ... but you'd need new shafts and gears, not just the synchros n' stuff in a standard rebuild kit.
On a totally unrelated side-note... This ad to the right of the Quick Reply is giving me the heebie-jeebies: "SENIORSIZZLE.com! Sex partners in the prime of life!" Ugh. I think I need to go poke my mind's eye out with a red-hot soldering iron...