Cleveland Models
http://www.clevelandairline.com/ has plans for an Aerocar. There were 2 versions of the Aerocar, one was 3 wheel, the other was 4 wheel. I THINK the one Cleveland has is the 3 wheel model.
Cleveland plans were originaly designed for rubber power, so some beefing up will be required. On the plus side, Cleveland plans are USUALLY quite detailed.