The .75 size engines are meant to slightly over power a .61 size airplane. The Tower is a good running, ABC engine.

I would try a 13-6, 13-7, or 12-8 prop.

The Tower .61 has been reported to be the Super Tigre .61 built in China from ST tooling that was bought by Great Planes. That being the case, I would suspect the Tower .75 is an ST .75 with a purple head and a Tower logo on the bypass.