Basic research, ah like looking at various companies throughout the world, that offer 2 & 3 cylinder engines (a couple of countries have big markets for this, and are in 3 wheeled vehicles, but that would require a simple search to find this out). And as I have said (but you would have to do a search) license the right to build the engine themselves, thus saving them (Elio) money.
How do you know that since 2008 Paul Elio and his team have not thoroughly researched other engine options they could source directly or license and build themselves? It appears to me that you are making a very large assumption about what you believe they have not done and what the results could be.