Don't count on it being THAT much lighter. Bored out means larger piston, probably larger conrod, maybe larger crank, so on. So, that weight tends to come right back in other forms. However, it shouldn't be much heavier (if at all) than the .61, if in fact it is a bored out .61.

I've seen guys fly them with saito .72's and .82's, so I don't see why it wouldn't fit! Needs to be propped down, probably--like a 14 X 4, or 13 X 4 (not sure which would be best for this particular engine), but I wouldn't go over a 4 inch pitched prop because of flutter problems and so on.

Good luck..
Hope this helped.