There are “sleeper” musclecars and then there are “ultra-sleepers.” While it is known that 1968 Impalas could be ordered with the 427 SS package (1,178 were produced) with either a 385-hp or a 425-hp big-block, few are aware of the other big-block-equipped full-sized Chevrolet’s. In fact, only 568 L72 427-cid, 425-hp V-8 engines found homes in the big cars, and it is believed that a scant 124 of those were dropped into the plain-Jane Biscayne! Add in the brilliant Butternut Yellow exterior, bench seat and an M21 four-speed, and you have this very rare sleeper. This particular example also features 4.88 Posi-traction, F41 suspension, power steering, tinted glass, AM radio, accessory gauges and a copy of the original window sticker. Showing only 13,700 miles, it is believed to wear some 70 percent of the original paint and shows minimal defects. One will likely never see a finer rarity.