I had the same problem.I ended up with 1 1/4 ounces added to nose even with all micro gear.DON'T worry about adding weight to the nose to gear the balance correct.The CG is "very critical" or it will be way to squirrely.
Wish I had opened up the fwd section of the battery bay before I glued the fuse halves together, that way the battery can be shoved farther fwd.
My P-51 has at least 20 flights on her at 18oz flying weight and it flies fine
My CG is approx. 1/2 inch FORWARD of bamboo spar.
Good Luck