Well to start they look like this:
Built by Quantum Sports Cars in Kingsbridge, Devon
The kit is around £4800, with an estimated build of £5500
If you are looking for any other cars that will utilise your XR2, you could try a Harlequin Jester. I little cheaper to build than the sunrunner and apparently one hell of a good handling car.
I did hear a story of one pi**ing of a few 911 Turbo's at Oulton Park (?)