Tom - thanks for your reply. I am very conscious of managing weight whilst building, particularly aft of the Cof G and even more so at the rear of the fuse. Being conscious of it and achieving it are two different things though and I appreciate your comment.

I note these engines have an oversquare cylinder so that helps torque and from your experience its seems that the 7-77 may just be a good choice after all! I'm not sure that 10% more displacement will deliver 10% more power but its got to help. Unless I've missed something of course!!

This won't be quick build but I'll keep the thread informed . . . . either way.

Dave