The big brake conversion may not mean what you think. Swapping 320i rotors and Girling calipers does not change the diameter of the front brakes, but actually changes the setup from unvented to vented disks. Since one of my stock calipers was seized I decided to do the swap. I had the calipers already and called Dave Varco at Aardvarc Racing to send me the hubs, rotors, bearings, and wheel studs.
The swap is very easy. Disassemble the stock setup.
Pack the new bearings and install the 320i hub.
Trim the dust shields for clearance and install the new calipers.
One of the problems with the swap is that the stock 13″ wheels no longer fit. That's actually a benefit though because my 15″ Rota RBs with Yokohama S-Drive tires look much better.