hi tezza,

The tornado pointed  has worked with a 20HP briggs and Stratton 4 stroke engine.
With 1/2 ratio gear between Crankshaft and multiwing fan.

I think you can try to use your old engine, but
 it is necessary that you builds lightest possible.

Also you need to adjust the scoop for the air near of your blade.

Thank'you to posting in the forum,
Happy to help  you

Pascall