Norm:
To capture the "stampede" concept, I would personally envision a number of vehicles all running across the open plains - very much like steer - in the manner of a stampede.The background could be a large scale map of the states - with the cars in a big swarm running across the staes that they will be crossing. The cars could be Pinto examples from many years, many colors, coupes, wagons, cruisers, special interest....
I'm no artist, but if I was to capture it, that's what I would do.....
The example you show is truly artisitic, and the artist certainly talented, but the flavor of the Pinto (as well as the stampede concept) gets somewhat lost in translation. The Pinto isn't typically a monstrous, fire breathing catapult as some other classic iron might be considered.
My thoughts, FWIW.
Chris