If it's really a Trainer 40, I believe the CG is right on the spar. It's also not critical. When I was learning, I played with the CG quite a bit, and could never tell the difference 1/2" forward or back from the recommendation.

By the way, while you're rebuilding, beef up the fuse near the tail. The tail will break off if you as much as look at it sideways.

[edited to delete gratuitous comments about the plane's design]