Someone asked about the cowlings, so I asked the owner. This one is a 310 Turbostream.
"Jack Riley produced variants of the Cessna 310 to improve performance. The Riley Rocket 310 and the Riley Turbostream 310 replaced the standard Continental 310 hp (230 kW) engines with Lycoming TIO-540 350 hp (261 kW) engines. These turbocharged intercooled engines were installed with three-blade Hartzell propellers in a counter-rotating configuration to further increase performance and single-engine safety. At 5,400 lb (2,400 kg) gross weight the aircraft had a weight to power ratio of 7.71 lb (3.50 kg) per horsepower. This resulted in a cruising speed of 260 knots (480 km/h) at 18,000 feet (5,500 m) and a 3,000fpm rate of climb."