There are 7 cases that make up the crankcase. They are the bearing case, gear case, front case, middle case, rear case, induction case and bell housing. The front, middle and rear form the core to which the two rows of cylinders are mounted. These three need to machined and strapped together for machining the flats and profiling between the flats.
The interior of the front case turned to finished dimensions. The case is 7 1/2 in round and the internal cavity is 6 in. In the picture you see it mounted in the 4 jaw chuck on my Southbend 10k lathe which has a 10 in swing. The lip you see in the image is concentric to the bearing cavity in the center and mates to the middle case to keep all three in line. The bearing cavity has a press fit to one of the two SFK-6005 main bearings in the engine. The other main bearing is held in the rear case.
Flipping the case over caused the lip to land on the non ground part of the chuck jaw so I could not rely on that to square the front of the case to the rear. My solution was to use 8 magnets, 2 per jaw, to create a standoff so the lip was not in contact with the jaw as seen in the image below.
The front case is turned to finished dimensions ready to be mated to the middle case behind and the gear case in front.
The step near the outer edge is the mate ring for the gear case and the step on the outer edge is a 7 in diameter reference surface which will be used later during profiling. The profiling will be just below this so it will be machined away.