RE: How much motor to fly this?
If a commercial A/C is sold as convertible, it has been designed to withstand the vibration level of a glow motor. But that is not what I would define as electric to glow conversion.
LASER cutting tools have permitted cutting out much material that is not needed for strength. But as you say they are not very crash proof. My lazy Ace is 11 years old. It has been repowered 4 times and crashed many times. But all I had to do was glue the pieces back together.