I had a look at the wrecked Lucas cam ring, does not seem to be a complicated job. They did not have CNC at that time and I say you don´t need today, just a mill with DRO for easier life - plus a dividing head certainly for milling the larger inner diameter. This is 42 mm on my part, the smaller diameter is 40 mm when the breaker heel slips over it in open position. The 42 mm i.d. does not matter at all as it never gets contact with the breaker heel. My idea would be to have the cam ring clamped in the dividing head in a ring for milling the 42mm circumference, the 40mm diameter was turned before already. So then the end mill will do the 42mm face and by leaving the circumference down from top end mill position, the black circle left top in my photo, and reaching same 42mm diameter at the bottom position, the other black circle. That way you will mill a bit of a flat face opening ramp down from top position and same at bottom position forming the closing ramp too. After this do a bit of handle swirling for more of the 42mm diameter then position the dividing head for the second angular position required for the 50 deg v-twin.
For fabricating new cam rings I´d have some through hardening tool steel , not a lot of distortion to be expected then and not a real effect on timing form this even with a bit of distortion.
I cannot tell how they positioned the cam ring in the mag end cap for correct internal timing. It is glued in in the old part I got. There is a milled gap down below but no indication how this engages anywhere.
Anyway, I believe old and worn cam rings could be reconditioned by having a special carbide end mill suitable for hardened steel and lick up the worn opening ramps for exact timing, no need for milling the rest of faces. Then a jig might be useful for pressing in the cam ring at the wanted position - or maybe glue that, cannot tell what was original.
But really I do not want to start a business at 70 plus of age, just saying . . . .
Vic
P.S. never seen face cam types, would think to be awkward to machine ??