Hi mate, if your putting disks on the rear, my advise would be to use a bias valve. But what I am doing, and what some others have done on here, is to remove your rear compensators & ABS, and supply a fixed pressure to the rears. Admittedly, this is a more track set up, as you don’t need to consider rear passengers, which will increase the weight. But if you hardly ever take back seat drivers then no probs.

Some people will say don’t use one, and for them, it probably works, as physically it will work without one, but the percentage of braking to the rear will increase the moment you put the rear disks on, so you need to allow for that, hence the bias valve.
Admittedly i was going to do my set up with out a bias valve, until i decided i was going to go for the set up which is taking place!

Also i would suggest upgrading the fronts as well. Maybe to the cossie stuff at a minimum. As having bigger stuff up the front will help to lower the percentage braking at the rear, helping to keep the balance.

Good luck mate, hope it all goes well, get some pics up when your done.

Cheers