RE: 8.8lb plane with a .61, how will it fly?
It won't be a rocket ship for sure. Long ago before I gave up on 2 - stroke engines I had a Goldberg Chipmunk @ 8.5 lbs. - OS .61SF. It pulled it along pretty good. I am now flying a VenusII @ 8.5 lbs. - OS 120 FS and it is just about right.
It will fly and do some aerobatics. If it is all you can swing go ahead and be happy. If you desire and can afford more go for it.