I don't think the turbo version would require an upgrade. It's always been in the back of Paul's mind and everybody else's that this thing would scream with a turbo, and IAV engineered a hole and bolt holes into the engine specufically for this purpose. So obviously the engine itself is robust enough to support at least a moderate boost turbo. After all, it won't take a whole heck of a lot to change 55 horsepower into 70 horsepower and watch the little puppy scream. Arranging all the appropriate plumbing and the exhaust routings might get tricky, but I think the engine itself would work just fine with the turbo.
You all may recall that IAV was actively playing with a turbo for it before the first engine was built.