[murray]

ian
i have done this before on a datsun off road sedan
i used stainless weld rods
in the book how to race prepare off road racers 4 wheel drives and baja buggys
it shows the welding of spider gears and side gears to the carrier with silicon bronze not realy welding but more arc brazing
where your problem lies is all the disimilar metals and heat traeting
yuo will have to pre heat the weld area to at least 150'c
if yuo go down the mig method i would disassemble the diff
weld gears and side gears ie pad weld these units accept for were the gears mesh if you have a oven post heat and let cool down slowly
reassemble and weld the side gears into the carrier preheat with torch post heat wrap in heat blanket to cool slowly
welds to carrier to start and weld to center so 4 weld on each gear so the weld end ont op of each other ie outsides to center this will help to stop cracking at weld craters