The Road Runner was Plymouth's 1968 idea: take a basic B-body Belvedere, fit it with the 383 four-barrel HP engine, license the cartoon Road Runner from Warner Bros. (with the famous Beep Beep horn), and price it under $3,000. The car landed at $2,896 base — substantially less than the Pontiac GTO it was aimed at — and outsold expectations. Plymouth had projected 2,500 units; sold 44,599.
Designer — Plymouth Studio under Chrysler corporate-design VP Elwood Engel. The 1968 B-body restyle (shared with the Belvedere / Satellite line) is the Coke-bottle generation that ran through 1970. The Road Runner-specific addenda — the cartoon decals, the bird horn, the matte hood option — are Plymouth-program decisions on top of the base body.
The 1968 K-code 383 was rated 335 hp gross. The Hemi was a $700 option that pushed the car well over $4,000 — only 1,019 buyers ordered it. The convertible body wouldn't join until 1969.