Mine needed no welding to the backing plate.
Here is the shackle.
Here is how it looks mounted.
There is also a need to shorten the collar on the rear axle sleeve to alaign the chain. Notice the sleeve on the left.
I used the 1963 type brake and it required some frame surgery for the large lip on the backing plate. If you use the late 1958-1962 brakes no frame surgery is needed.