A 60' span is probably beyond the reach of a conventionally joined timberframe structure, particularly given today's building codes. However, large trusses can be made with the addition of steel shear rings, plates, etc to carry the stresses in the joints. I have some experience with spans up to about about 30'. Not quite what you need.
However, Ben Brungraber has done some research on the old building methods, and has a number of references on the old metal plated, wooden trusses. I expect he would be a better source on this one.
