91
Lest we forget, there was a topic created quite some time ago specifically titled "Swords Into Ploughshares" that might also provide some inspiration to this GB.
Replace the original SCUD missile with a large cannister of similar dimensions to the original missile and call it an upgrade to a new weapon system that was designed to replace the SCUD missile. As for physical details, well, leave that to their collective imaginations.
Perhaps a more British Sabre Dingo carrying two Firestreaks or Redtops and using the same radar fitted to the P.1109 and the HUnter that trialed the Fireflash?