Thanks for your reply. I am changing the shocks and springs all round, and problems with discs etc have come to light during these works. I have no idea what the discs are, as they and the 4 pot brembos were fitted by the previous owner .The wheels are 7 spoke Ford rally sport. 17 inch wheels are not listed for 3 door RS Cosworth. Generally they were 15 and 16 inch. Just looking at options to do away with the spacers. After speaking with a reputable brake specialist, bells and rotors seem to be the way to go. I can then retain the existing wheels and calipers.