ORIGINAL: andernamen
My TF P-40 CG was set with the plane level according to the manual. It was tail heavy and flew like crap. Set the CG according to the manual, but make sure the nose points at a slightly downward angle. You shouldn't have any problems and you can adjust later if you need too. It shouldn't be too far off.
Agreed. Usually the manuals are a good spot, but I tend to put mine a tad nose heavy from the manual just to be safe. On the H9 1.50 P-51, manual says 6 3/8" from LE against fuse. I got it balanced at 6 1/4" with a bit of nose down on the balancer.