Make the connection

Dan Gurney ?

....the backer-board they're sitting on. 

Posted by: @franklemire

This is an easy one to start with

 

What connects these three cars?

Dan Gurney F1 car 1967 Belgian GP winner on the left, Gurney and Foyt 1967 Le Mans car winner in the center and A.J. Foyt Indy car 1967 Indy 500 winner on the right.

@john3976 Right so far - there is one more connection.

Posted by: @franklemire

@john3976 Right so far - there is one more connection.

The only other connection I can think of is all three were American built. 

I know Shelby and Gurney partnered to form AAR All American Racers. 

I don't know of any connection between Foyt and Shelby outside of driving for Shelby. 

All three cars were naturally aspirated.  

@marty-johnson Wow! that is even more technical than I was going for but you zeroed in on the right component.

@franklemire - Originally, I wanted to say that all three cars were powered by Ford.  However, the Gurney F1 car was powered by an independently built 12-cylinder engine.  Hence, I retreated to the only other element that was common among the three cars.

@marty-johnson You are correct and I am wrong - I had taken this photo a while ago and thought I had Gurney's Indy car in the picture not the F-1 car - my mistake! Great answer! - I'll have to be more careful with the next one.

The Eagle was powered by a V-12 Westlake engine. The Foyt Indy car was his second chassis built by Foyt with it using a Ford engine and of course the Ford GT40 MKIV was designed and built at Kar Kraft making it an all American built and powered race car. 

The turbo era had not yet taken hold in Formula One as it was still over a decade away. 

So I have to say that the most correct answer on the three was all three were American designed and built chassis and all three won big races in 1967 and all three were driven in those races by American drivers.