Vac forms aren't allowed in the class. I think what Dave is after is something with a high enough rear deck to clear a side or angle winder. Most aerodynamic LMP cars have a low rear deck, indeed some models have to have a hump to clear the contrate gear when in inline configuration. A front engine Panoz has quite a high rear if you don't mind cutting the interior detail. However in my opinion Dave is quite quick enough with what he's already got.
Allan

Allan