Getting a sure grip or like diff. for it is not hard and ratio's are limited in the upper 4's and beyond. Like above, being it is a c-cliped rear end, you'll need to address that if the performance level gets high.
I'm not sure about stronger axles for it, but you could inquire if need be. Theres several company's out there for stronger axles. Shortening the rear is a catch 22. By the time you spend the money on shortening the rear, it would have been easier if not cheaper to purchase a DANA 60 for it. Which can be had new from 2 places.