That was back when most race cars that ran at Indy were front-engined using the four-cylinder Offenhauser engine. The success of the rear-engined race cars from England forced Indy racer designers to go to rear-engined cars by the late 1960's.
They should have just banned the F1 cars. How many sanctioning bodies have they run through now for Indy? I remember USAC, CART, and IRL. It was USAC during the British Invasion.
I only got to one open wheel race - as I recall, Andretti won the one I saw.