Ascars at Knockhill!! In the wet!!!
Ok, only kidding.
The track would have to be Oulton Park (full circuit).
The line-up would combine the best of FIA GT, Gold Cup and national series...
Race 1 (20 laps) - PCGB Pirelli Porsche Cup circa 1998 (i.e. when it was still for all Porsche models, before Porsche GB realised the 993 was quicker than the 996...

)
Race 2 (15 laps) - 1950s/60s Grand Prix - Maseratis, Ferraris, Lotii
Race 3 (10 laps) - XR Challenge - XR2s, XR3s, nothing like a bit of banger racing for light relief...
Race 4 - (1 hour) FIA GT Open (all classes 1995 to present) - Porkers, Macs, Saleens, Vipers, Ferraris, Bentleys, prototypes, preferably without 2002's carnage at Nickerbrook...
Race 5 - (20 laps) 1980s/90s British Touring cars - the golden age of tin tops, from Rouse's Cosworths, through Volvo estates to the Audi Quattros and Nissan Primeras.
Race 6 - (1 hour) The BIG one - 1960s GTs - Astons, E Types, 250 GTOs, 275s, Mustangs... the ultimate multi-million pound race, the highlight of the best years of the Coys Historic Festival at Silverstone...
Given two endurance races, I think six'll do... Besides, can't think of any more.