Steve,
I have a 3W-157 in my AMR 1/3 Waco and it s more than enough power. It will pull it through huge loops. I beleive the AMR kit builds heavier then the Barth kit as well.

I crashed mine last spring and it is going thru a total rebuild at the moment, nothing wrong with how it fly's just pure pilot error. Gotta keep power on during final, too slow will get you in trouble.

Later!!
Anthony