1. mount the casting with its back out and cut the small step on the back.
2. with the front out,
cut the larger step,
face the hub so you leave the whole top face just planed over.
(cut a little high, then another 1 or 2 cuts of 0.01 mm until it looks right).
face the tyre 1.7 below the hub.
bore the centre just under the size of the final reamed diameter.
3. with the back out, face the back to your chosen the tyre width.
4. mount the casting on a slightly loose (by diameter) mandrel between two discs, centre it, tighten up, and make the final cut with a form tool.