Update - 30/03/2009
Rear Calipers arrived today, HUGE! Should definitely stop the rear end no problem

Will measure to see if they take Solid or Vented discs, either way they'll be more than enough to stop the rear end of a 600KG car.
Had word from the powder coaters mentioning they weren't too happy with how some of the parts came out, so getting them back tommorow.
David