Actually for the basics like this you can use the raw theory. While I agree that our selected size affects some things the nuetral point calculation and resultant CG selection is pretty cut and dried and scales faithfully. The only difference being that for full size stuff they insist on a far larger %of stability than we do so full sized stuff often will call for much more forward CG's than us modelers use. But that is a choice and has nothing to do with the physics of scale.

There's some MAC and Neutral point calculators linked in the sticky thread titled Aerodynamic Tools, Calculators and test links. Check 'em out.