Hi down there! I just did this conversion. The calipers I used were off a '91 Toyota 4x4, casting # S12. The vented rotors are '84 300zx. The rotors need to be turned down -3 mm on the outside. Next you wiil need spacers to move the rotors inboard about 17mm if you have '72 hubs. I made my own because the ones they have available don't centralize the rotor concentric to the hub, they are just a flat p.o.s. The 280zx master is marked 15/16" on the casting where as the early one is 7/8". Not sure if the Sumitoma is the same casting, things being different in the various foriegn markets. I also put the 280zx discs on the rear. Noticably better stopping but will have to try high speed fade before I brag to much.

 

I mean that the over all length of the new rotors is 17mm shorter than the stock ones. If your doing your '70, the length is 19 mm shorter. This length is also called the "HAT DEPTH." For a picture go to Ebay motors item #2444441850. As for the machine work, I am refering to the largest diameter of the rotor needing to be reduced so it will fit better in the caliper. It can rub on the outside of the new rotor.