Hi!
The OS LA series of engines are perfect for small scale models as they are very reliable and very lighly built.
I would choose either the. 40 or .46 LA depending of how big the model is. I would not choose a ball bearinged engie as those are heavier and are a little more expensive than the LA.
Those that say that "you can always throttle down" don't know what they are talking about ...that simple
When building a scale model outmost lightness and adequat power (Not max power)is of vital importance.

Regards!
JanK