Take the rear end apart completely.
Center punch and drill a hole in 4 equal spaced places through the center housing and the axle tubes.
Get 4 carriage bolts per side that have a rounded head on them. or any blt with a thin head.
stick the bolts through and tighten nut on them.
Clean area to be welded thoroughly
Now you are ready to carefully weld the axle tubes to the center housing.
Careful now and remember that heat pulls the metal so keep the heat as even as you can all the way around the housing. That usually ends up with short stitches of welding and across from that stitch you do another short stitch and keep alternating back and forth until it is all welded.
Last you can tack the nut to the bolts you stuck through.
Purpose of the bolts. Far too often welded housing tubes fail and the weld breaks. The bolts will act like 4 pins on each side giving additional strength for the weld to hold.
Ed