The GTO’s original 389 four-barrel had been replaced at some point along the way. By the time Cap and Robin purchased it, a 421 fitted with Tri-Power was nestled between the framerails. Now displacing 454-inches, it was stuffed with a stroker crankshaft and forged connecting rods and pistons. It inhales though a set of ported No. 62 cylinder heads and a Barry Grant Six Shooter induction system, and exhales though a set of H.O. exhaust manifolds and Flowmaster exhaust.