About the same as Citroen in 1955 (also without computers). Their underside is not completely flat, but is slightly concave for aerodynamic reasons. The muffler is inside the ladder crossmember under the front seat, but the tailpipes and engine pipe protrude below the floor. What is notable is that the underbody space is smallest between the front wheels and nearly doubles from there to the rear bumper, again, for aerodynamic reasons. Giving a car of almost 50% higher mass than the contemporary Holden, but with a top speed 20% higher on less power (150kph on 60hp).
John

