I understand the desire for an off the shelf solution. These engines are made in large quantities and are priced accordingly.However one of these would not do it. Two is a bit of a stretch and how in the world would you mount two. Sounds like some serious engineering and weight gain.There has been some success with the larger V-twin engines. Often found on generators. They start around 22HP and go up. One is commercially available, ready to go, with prop and reduction.look up culver props big twin engine.It may represent a bargain with all the work done, but it is not cheap.Tom XL-7
Would something like this work? http://www.northerntool.com/shop/tools/product_200514299_200514299I don't want to spend $5,000 canadian on a hummel engine and it looks like this guy used that engine with a reduction drive for his aircraft 40HP at 5500 rpm doesn't sound too bad for $2000.