Not hard.. just messy: Here is only one utube.
There are 4 bolts holding the 'backing plate' to the axle. Remove and you will see the area clearly.
When welding a small mass to a large mass (the axle has a lot of steel, the plate doesn't), the large mass needs more 'heat' than the plate. I usually heat the area with a torch then quickly start welding...
Careful, do not get the axle too hot as it can affect the rubber rods in the torsion axle... that will take a LOT of heat or incorrect use of torch too close to the pivot.