Just looking at that pic, it looks like it might have some up thrust. (Look at the line of the muffler in relation to the wing saddle.)

Does it still fly tail-heavy when the power is off (gliding)?

Thoroughly check the vertical and horizontal thrust lines and correct until it is either at 0/0 or a very little bit of down/right.

For what its worth, my JKA P-51D flew rock solid from the start with the CG 1/4" forward of the recommended location. So, your's should too.

Also, check the angle of your ailerons at neutral. The bottom surface of your ailerons should follow the line of the bottom of the wing's airfoil.

HTH,
D