Cockpit width is the only thing I see...
I am really excited about the new Le Mans "GT-Prototype" regs... I love the old Porsche GT1 and Merc CLK GTR (last time I went to Le Mans those were the cars that were running; 20 years ago!!! )...
....But those new rules don't work for the MVRC; they will design their cars to a set of target aero coefficients and then they'll be balanced up to equal aerodynamic performance (presumably using gurneys amongst other things).... That's the only way to get the cars looking more pleasing to the eye... But no good for an aerodynamics competition...