Iain,
The car you are referring to is AMGT-2 raced most famously by Aussie Paul Hawkins. Apparently owned now by Jack Launtz a member here (Driven) his last post was on 28/6/06 here:-
SAAC At VIR Next Weekend, July 1,2
There is also contact info in this thread:-
Info wanted on decal of XGT-1