I have heard of others that thought that this plane didn't fly that well. Everyone of them said they had put a smaller engine in it.
I highly recommend the 120. I put and OS 120 with a slimmline smoke muffler. Is a great plane with that combo. the difference in the price between the 91 and the 120 is about 100 give or take. Higley's book can be bought through Tower I am sure. You have to build up the firewall and the stringers as he suggest for the 120. Also this engine helps to balance the plane, it needs nose weight so stick it out as far as you can get it. Without making it look lousy. Why add weight latter when you can do it w the engine. I did almost all the changes Higley talks about.

DiBo