It's the Douglas A2D-1 Skyshark, a turboprop aircraft derived from the A1D Skyraider (and intended to be its successor), powered by a 5,500 hp of the Allison XT4O-A-2 turboprop engine driving a contra-rotating double propellor (the turboprop exhaust providing additional thrust), more than doubling the 2,500 hp of the Skyraider's Wright R-3350-24W engine. The problem with the engine's reduction gear was never satisfactorily solved, and only seven aircraft were built.
The only known surviving Skyshark is BuNo 125485, which never flew. Instead of being scrapped by Douglas, it was used (minus its engine) for ground radar calibration at the Los Angeles International Airport, and was later given to the Planes of Fame museum.
The A2D was actually 3.5' longer than the A1D, due to the 26' length of the X4TO-A-2 engine.
The picture below was taken at Chino in 1981; the plane was at that time awaiting restoration:
