That's the same I did but ended up with a 4-cell and a 5-cell in the engine box along with 9 1/4 ounces of lead. This is the strangest plane to balance I've ever owned. Seems like everyone has a different setting and needs different weights. The only variable I can come up with is the tail wheel. Longest moment on the plane and, the only thing that doesn't come with it. Here's the one I used.

http://www2.towerhobbies.com/cgi-bin...?&I=LXBN42&P=0

Pretty heavy.