In 1969, Ford introduced the high-performance Cleveland 351 V8, designed to replace the 351 Windsor. With higher-flowing heads, 4-bolt mains, and different cooling and oiling systems, the Cleveland engine was ultimately only produced through 1974 while the Windsor V8s lasted through the late-90s.

Shelby production ended shortly after Cleveland engine production began. Thus, there was never a Cleveland-powered Shelby vehicle sold to the public, although they did build a test car. Hemmings Auto Blog says that this one-of-one Cleveland-powered Shelby GT350 is being put up for auction by D.E. Foeller sales. What will this weird Shelby sell for?

This 1969 Ford Mustang was supposedly once owned and built by Shelby’s chief engineer Fred Goodell, and rather than using the Windsor-built V8 engine, Shelby opted to try the all-new Cleveland model. Shelby also installed the interior for the upscale Mercury Cougar XR-7, replacing the stalking cat with a coiled snake.

One of three development cars, this was the only prototype to escape destruction. It was also said to have an experimental fuel-injection system at one point, though it uses a standard carburetor setup as it sits. The car was sold during Mr. Goodell’s estate auction, and has since appeared at big car shows from coast to coast. It should bring a pretty penny when it goes up for auction this July.