Here is my procedure for welding diff's
* clean everything very well with brakeclean
* let dry
* heat carrier with torch (or put entire carrier in the oven at 450* for two hours)
* weld spiders to the carrier, both sides
* get small nuts and weld them inbetween where the spiders mesh together
Hints:
* if you leave the carrier in the axle, fill the housing with water and leave the pinion points down - this will keep the pinion seal from getting hot
* if you leave the carrier in the axle, pull the shafts. You don't want slag on the axle splines
* let the gears/carrier cool slowly, don't quench with water
* clean everything very well after welding.
Good luck, works great!!!!