OS.10?

I run a G90, a Pitts and no tail weight. Theres nothing wrong with adding a bit of tail weight . You will find many who run a Saito 100 which is a good combination. A Magnum 91 is not a good engine for this plane id you want performance. That 91 puts out about as much umph as a 60 2 stroke which will fly the plane as your aware of but nothing to brag over.

A Saito 82? You may as well keep the Magnum. Sounds like you want your Shoestring to be a hot little flyer. Saito 100 or 90 2 stroke is your answer