Heat up slowly to just before it starts to glow more of the yellow color then bright orange. Weld with NIROD (Nickel Rod) then warm the area after welding shorting the heat times over about 1/2 hour for that area. When you heat during the cooling cycle you do not want to bring it to the glow point only aiding in the slow cure cool.

Also that area of the Diff Housing is the thinnest so be careful with heating. I would build a truss off the tubes to that area and then attach your mounting point.

Good Luck