BB, I have a 'scale Aviation modeller' magazine article (Vol.7 Iss.6, june 2001), where Bill Clark made a Spitfire F.21 with contra-rotating prop in 1:48 scale.
He combined the Aeroclub F.21 conversion kit fueslage (the one designed for the Airfix Mk.22/24 kit - they make two conversion sets for the F.21), with the wings and contra-rotating prop from the Airfix Seafire Mk.46/47.
If you want a copy of that article, drop us your address in a PM!
Evan