I have to agree with Missleman on this. The plane is not designed for that engine size.

You are starting off with a FAR BIGGER prop as suits that engine.

That 16x8 is going to mean a lot more torque on the fuselage framework, if you forget about everything else.

You may get a rocket like flight or two, but there is good likelyhood that the fuse is going to undergo damaged with each flight.

You'll also notice quite a bit of roll induced as you run the plane up in flight, yaw at take off will be more problematic, one wheel is going to get more force, and the list goes on.

If the plane were a bit larger....

While the BHP ratings make the engines look somewhat similiar, this can be deceptive. The gas engine has a bigger more massive cylinder head allowing it to turn that larger prop.

Even if the engine runs smoothly, a lot more energy will be transferred to the airframe with each stroke.