I have successfully straightened diff housings before in a couple of ways..
1. pull it out and get it straightened in a press, best way to get it exactly how you want it, did this with my old rally car after it gained a few degrees of neg camber after launching off some major yumps..
2. use an oxy torch to heat the tube cherry on the side you need to shorten, then quench with a rag soaked in water, by doing this carefully you can "pull" the tubes any way you want, just need to keep measuring it to make sure you don't over do it. Can be done in the car as long as you are careful with the oxy, KEEP A FIRE EXTINGUISHER HANDY! Did this quite successfully with an Escort Atlas housing that had quite a tweak in a prang, got it back well within spec in half an hour.