I think the 51 is a bit heaver then the 46.
Also I think the plans show a LA 40 or 46, so I think it might have been designed around the OS engine.
You can do the whole pattern in just about 4oz. 51 might burn more?
You could always set it up for both and see if one is better then the other, burns less fuel ect.
It will not be a hangar queen if you build it.
And yea Lou's Bear Tut2 is killer!