RE: O.S. Engines-Model differences???
Get the Goldberg Tiger 60 and stick a 90 size 2 stroke on it and you won't be disappointed.
I tried an OS 61 2 stroke, an OS 91 surpass 4 stroke and a Super Tigre 90 on mine and I like the Super Tigre 90 2 stroke the best.
The Tiger 60 is a smoothe flying plane and flies like it's on rails.
Have fun and good luck.