I ran across this site and it has some good detail on the pictures if you zoom in on them you can just about see entirely how it was built.
TTW - GM Lean Machine
It looks a lot simpler than the carver and would probably be much easier to make at home. Use something like a sport atv with a 650cc or so engine as the back end and make the front end out of mild steel tube with that center pivot shaft made out of structural steel.
All of you guys thinking of making trikes ever consider something like this? The tilt and steering could even be hydraulically controlled using something as simple as an arduino to control the tilt and wheel steering based on speed. Or it could simply have steering like a motorcycle with the front wheel set up so it can still be counter steered in a turn.
GM calculated that,' steady-state fuel consumption of more than 200 highway mpg, with an EPA combined highway/city rating of 150 mpg ( Road and Track 1/1983 ).
here is an article on how a tilting trike handles:
Three-Wheel Vehicle Handling Characteristics