I would face off one end while in the 3 or 4 jaw and put in a ctr hole. With tailstock support cut the fins while you have plenty to grip on.
Then reverse in the chuck, rough face, ctr drill and with tailstock support form the flange and waist above it.
Finally remove tailstock, drill then bore to finished size and then take the last skim cut off the underside of the flange to bring ot to final length and ensure it is at right angles to bore.
I'm assuming the flanges are left with flat edges not rounded over.