Which Bipe do you have?

What type prop, size and rpm was the Webra turning. I'd compare the numbers to reported numbers of other engines. You will indeed end up with a heavier model with a gasser. I'd suggest your looking at close to an additional lb. dependent on what engine package you choose, maybe even more.

If the plane is 10lbs. I'd be surprised if the 3W 24 would not do what your looking for...