It was designed to use your stock rear brakes. If you have an earlier kit, it could have been put together by about anyone and could be about anything.
Rear big brake kits are a relatively new item with Stoptech introducing the first rear big brake kits about 20 years after the Z32 was introduced. The reason for this is that they are not really an upgrade. Stopping faster required less rear braking due to the weight transfer to the front axle. I ran some quick numbers: