The relay they sold you is most likely a changeover relay, having the extra contact(centre one) which will no doubt be numbered 87a, it's next one on outside numbered 87.
So long as the pin positions are the same, it will work, ford have had a habit of using changeover relays in place of SPST single pole single throw, ones.
Why are you changing it ?, why not just come round and get it re-wired, won't take long and peace of mind then, but not just yet as have SWINE FLU!!
tabetha