The things you do to keep out of mischief.....

[Surpmil]

It would be interesting to know how they machined that rad on the original brackets, whether a milling machine was used or perhaps a shaping machine.

If you mean the convex radius on top of the "cradle caps" it's a rough cast surface usually, sometimes worked over on a belt sander or with a rotary stone (N92 brackets) Some of the early brackets were very well molded and finished, but rough as guts soon became the norm it seems.