Hello guys and girls, I'm somewhat new to the art of machining so be gentle!

Ive recently purchased a small 5 ton injection molding machine called a rabit 2/3 and I'm looking to build my first mold. Interestingly, these machine take a 3.15" round mold X 3" total thickness.

Anyway, my question is how do you fixture and accurately locate a round object to be milled in a cnc. The mold halves need to be flipped to add features that match up with the other side. These need to be real accurate as you can imagine. I do have a touch probe that can locate outer bores and whatnot. I've gotten some 3.25" 7075 T651 aluminum that I am going to use as my stock. I asked the seller to include a mold with the sale of the machine so i could get an idea on how to make one. Attached are some pics of it, the platens, and a picture of my cnc machine that I built. Let me know what you guys like to do! I'm all ears and am eager to to learn from the masters!

Thanks!
-Will