I need to re-read the rules but aren't the major differences in engine sizes/restrictors etc? - not chassis construction?
Yes, differences are weight and engines basically
LMP1: 925 kg, 6 ltr. aspirated, 4ltr. Turbo or 5.5 ltr Diesel
LMP2: 775 kg, 3.4 ltr aspirated, 2 ltr. Turbo
height, width and length of the cars are equal for both classes, so I guess the chassis don't need to differ very much