I wouldn't do it still mounted to the axle housing. There's no reason to leave it on there except laziness. Pull the extra 10 nuts - it's worth it. And there are a lot of reasons that make it easier to do separate.
When I did mine, I set the whole thing in a milk crate (it was handy) with the pinion down so I could rotate things around and I could do almost all of the welding down (cuz I'm not the best vertical welder). I did not weld the gears to the carrier but did spend quite a bit of time filling EVERY void and around every contact point. I haven't had any problems with mine for the past 3 years and it's street driven almost every day. I do have to tighten my rear u-bolts every 6 months or so as the torque on the housing and springs making tight turns on pavement puts a lot of stress on them and the rear end starts to clunk around.
I welded mine because it was the original 10-spline one from my 64. I figured if I ever broke it (or the axles) that it would be a good excuse to upgrade to 30-spliners and a real locker. It just hasn't happened yet.
Stuff some aluminum foil under the carrier to cover the pinion bearing as much as possible to keep any weld debris from getting in there (and wash it out afterward as well). I used a stick welder for the big gaps on mine, so I had a lot of slag to worry about.
This is probably a 'no duh', but don't clamp your ground to the housing or the pinion. Clamp it right to the carrier if possible. A little arc within the pinion bearing or carrier bearings will destroy the 'economy' of welding your own. The 200 is plenty of welder - I wish I had that welder when I did mine.
It has its advantages and disadvantages. If you ever anticipate driving in snow or ice, I wouldn't do it - sideways in a hurry. It's cheap - only costing some welding rod/wire and a couple quarts of gear oil. If you still have drum brakes in the rear, it'll even out the braking forces between the rear wheels. The down side of this is that if you ever lock up the rear end on the street, the little flat spot will be on the same spot on both wheels and will thump until it rounds over. It's way more predictable both on-road and off-road than an autolocker, but will squeal tires around turns and accelerate tire wear.
. thanks
