Mine is a 1964 I with IO 470 U engines. I have read this was a very good engine. Before 1964 the exhaust went over the wing causing corrosion issues. 64 and up to I believe 68 used augmentor tubes to draw the exhaust under the wing and draw air thru the engine to cool it and not require cowl flaps. I think all 310s are good designs. Finding one that has been flown regularly and taken care of is the challenge. The older ones that I came across had newer paint and interiors than ones that were in the 1970s. Mine has a nice newer paint job and a new leather interior. It showed me that the owner cared and had pride of ownership. What good is a glass panel with a ratty interior that your wife, or girlfriend, won't want to be seen in. My plane was upgraded with new and newer steam gauges that I arranged on a panel that I manufactured myself. The engines are strong and it took about 3 months to shake the bugs out so I can just get in and go. Good luck with your search. Let me know if you have any other questions.
Regards
Kevin
