The plane in the vid is near 17 lbs before fuel. The G-62 is RC ignitions conversion and weighs 4 lbs 1 oz. The CF pipe and modified DA-50 header weighs 11.5 oz (if memory serves)
http://www.youtube.com/watch?v=Apz895e8ERw
Ralph says that the 62's like RPM as they are designed to run at 13K. They really do come alive over 7k.
One consideration is that you will be working the engine harder to carry the plane that weighs more and has more drag. As an educated guess you might find yourself using over half throttle most of the time so you will need to keep the engine cool to stay on performance. Also midrange torque will be less with the smaller engine/prop so getting out of trouble in manuvers might need more lead time.
I put an undersized engine on a 35% airframe recently. (Torch 90 on Pacific Planes 102 inch Extra) Power to weight is 1.7 and it will do most anything except multiple upline snaps. Recovery from these type of manuvers are slow and I think it is the lack of torque as the thrust is there.
Have you guys ever seen the vid of the 40% aerobat on a DA-100? It flew like a foamy as the weight was the lowest for that size plane. If you listen to the engine he is running it hard and long for the uplines and majority of the exciting part of the flight.
Good luck with it.
WrongWay