Apologies for my earlier misplaced commentary.
But now that I understand the problem, may I suggest that what you need made is actually pretty simple? Instead of this complex machining, all you really need is a 6 bolt adapter and a plate with holes for the four bolts and then screw them together. If you get the thicknesses close you can adjust the rotor centering via washer shims.
These are $6.99 on Amazon:
https://www.amazon.com/KIEVODE-Freew...3&gad_source=1
Then you need to take a flat plate (probably 1/8" mild steel) and drill four holes for the mounting bolt and 6 holes for the adapter ring. Then use 6 short screws to mount the ring to the plate from one side, and another 6 short screws from the rotor to the ring on the other side (tip of the screws nearly touching half way through the adapter). If you are laying this out and drilling by hand, oversize the holes a little so they don't have to be as precise. You may also need recess or countersink the hub side of the plate so the 6 inner screw heads aren't hitting the hub body. I don't think you'll need to countersink/recess the four bolts - they only did that to clean up the casting.
Once the precise stuff is done you would need to roughly cut out an axle clearance hole in the center of the plate and maybe trim down the outside. Lateral disc centering can be accomplished with washers between the plate and the hub or between the plate and the 6 bolt adapter. Washers between the plate and hub would also create clearance if necessary for the 6 plate-to-adapter screw heads.
If that wasn't clear and you want to talk about making an adapter out of two pieces, let me know.