RPO Z11 gave roughly fifty 1963 Impalas an aluminum front end and a 430-horsepower 427 that never appeared in a single Chevrolet brochure. The very first one built went to Dave Strickler, tuned by Bill “Grumpy” Jenkins. Here is what the option actually included, why its 427 has nothing to do with the famous Mystery Motor, and how the whole program died in a matter of weeks.