Ray Brownfield’s red 1966 Mustang convertible looks like a straightforward restoration until you ask which 289 is under the hood. Ford sold three completely different versions of that engine in 1966 behind identical fender badges, and the spread ran from 200 horsepower to 271. Brownfield has owned the car since 2005 and turned the restoration around in five months. Read on to find out why that single engine question changes what the car is worth and how it drives.