Wasn't able to find anything about it being developed for a helicopter, but did find an extensive history on the engine here, including a list of experimental aircraft it has been used on near the end of the article: Chevrolet Turbo-Air 6 engine - WikipediaI've got the engine, I am going to start there - need to insulate the 'shop' a basic 16x20 shed. Smaller than I want, but I think I can make it work until it all "comes together" The advice to do something daily is great advice --- keeping a project moving regardless of speed is a lot easier than restarting it --- I've seen it a dozen times in my life if I"ve seen it once.
The plane is 23 foot tip to tail, remove the engine and rudder and you get at least that much back. That will be _tight_ but it should be workable. Installing the motor likely will be the last thing I do before it moves to a hangar. We'll deal with that as it comes
The Corvair engine IS an aircraft engine -- I think that is why it has been so successfull, a lot of people don't know that -- it was intended to be used in a helicopter, but the war came to an end and Chevy was left with an engine they didn't know what to do with.
It was the subject of a lot of R&D during it's GM production run, and quite a bit more since, as several Corvair engine guru's have worked to make them dependable alternatives to the Lycoming and Continental engines most widely used in aircraft. Basic Corvair Information , Spyder Engines | Azalea Aviation
One note of caution if you are going to start with the engine. Corrosion is the enemy of engines that sit for extended periods of time without being run/lubricated on a regular basis. It can be minimized with some precautions both while building it and after. There are pickling strategies to use when building to keep moisture from exposed steel that will help, and something called an engine saver to keep the crankcase filled with dry air using a small air pump, and a large desiccant container to recirculate and dry the air. A relatively small investment to protect a relatively large one.
Have fun!