The solution to the Hummelbirds lack of Hp is simple enough.
A Verner V3 has 45hp genuine and 37hp at cruise and would look damn cool, comes with electric start and is reasonably priced compared to the Half VW.
Or even better would be the Pegasus 0-100 with 60hp and still similar weight to the VW. approx $6000 US.
With the Pegasus the performance would be a huge improvement.
Or a Hirth F23 twin with gearbox would work well.
A Rotax 582 would give plenty of grunt.
The radial cowl in the video looks great and can cover any of these above engines and hide the two stroke exhaust. And give better streamlining at the same time.
I have always hankered after a 'Bird but not with a Half VW.