ArtfulBodger.net
This actually should be the second picture, but the first is missing. In the first step, I mounted the casting's top lug (which is here being parted off) in the four-jaw. I centered the casting and faced it, leaving a raised center the diameter of the cylinder bore.

In this picture, I've flipped the casting and am gripping it in the four-jaw by the raised center section. Big...

More of the same: parting off the top lug of the casting. Big...

One finished casting, another still rough. Big...