So, turns out a didn't toast the diff at all- little bit of wear evident but nothing much. No, what I actually did was snap off the end of one of the driveshafts inside the axle ( they have dog-bone type ends ) so the all the power was going to the front wheels. I also toasted a bearing in the upper part of the axle, but that doesnt seem to have caused any issues since the same shaft it was on is supported by another pair of larger bearings.
All I have to do now is find a replacement driveshaft, steering rod & knuckles which isnt too bad at all compared to what I thought I would end up having to do.
Left hand side knuckle had it's little arm bend right back and twisted, I straightened it out a bit but both will need replacing.