The cheapest and easiest way is to use 2WD COSWORTH calipers and discs.The GRANADAS had exactly the same rear brakes and are more likely to be found in a scrap yard.
You will need. 1.COSWORTH 2WD CALIPERS
2.COSWORTH 2WD SOLID DISCS
3.COSWORTH 2WD PADS.
4.LONGER BRAIDED FLEXY BRAKE HOSES
5.MK5 RS 2000 HANDBRAKE CABLE.
Pics of my conversion painted red