LP 400 and early S cars are lower than all countach after late 1981
check the ILR and you will see that also early S cars (called S1 and S2) have lower roof and have a slightly different chassis (sharing the same with LP400), lower ride height, ecc.. the early cars are also some lighter (LP the lightest)
LP400 and S1, S2 cars are not wider, but they look wider because of the low roof-ride height

there are other differences btw an LP 400 and 5000s:
4 liter - 4.7 liter engines
instruments SW - Jaeger
door panels
mirrors
mouse hair dash-leather
and more