I've got about 80 hours behind a corvair now-and counting. It's in my (Jake Jaks) Pober Junior Ace. It's got the power to haul the 830lb airplane, two dudes, flight stuff, lunch and, 18 gallons of fuel. It burns 6gph at approximately 2700rpm. I've built many corvairs for dune buggies and couple aircraft engines (pre-nitride crank). No problems and very economical. However, if you go with a fast design it is recommended to add the "fifth bearing". This will add to the cost to build the engine obviously. As for the other "aircraft mods" their cost is in line with any engine. The crank will run about $500 to prepare. A new Airmotive carb will set you back a few bucks too. Other than that, you can fabricate most of the modifications (top plate, oil pan). Get William Wynnes information/plans. He has the info for getting machining and nitriding done in the plans book. FYI, you "can" spend $6500 on a corvair; but you don't have to.