RE: Rimfire 35-30-950
The 35-30-950 has a max. watt output rated just under 300watts. A scale plane would be requiring 90 +/- watts per pound of aircraft.
So in your example - 64oz. = 4lbs. x 90watts per pound = 360 total watts required - you would be a bit under mathematically.
I would recommend being somewhere closer to 40oz. with 48oz. as an absolute max. on a scale aircraft with that motor.