Racer,
I think to get the comparable power, you need a light weight 35 to 40cc gaser. My rule of thumb is that the gaser should have about 50% more displacement then the glow engine. The Brison is on the heavy side with its Sach cylinder etc. Besides a cub has a short nose and liftinf air foil. Weight shouldn't be an issue, since it will be hanging on the prop most of the time.

Dave