I have a Gladiator but have only flown it once. I used my trusty AME .049 that is very powerful with the gabreth head. The problem with my flight was the plane was very tail heavy. Also, there is no mention of CG in the instructions. I garuntee that any engine used other than a Fora or Cylone will need nose weight. This plane was designed around those types of high performance bb engine.
the AMEhad a lot of power and flew the plane just fine BTW. The need for the more up to date engines would only come into play on a ntional type contest situation. For local stuff, the leser engines would be fine. Also, check with Larry Driskal, kittining it together, to see if he is still making kits. Those designs are great. Especially for the lighter engines.