I don't know if Southern Elm is anything like the Arizonia Elm we have here in our subdivision, but if it is, It would definitely be a good wood for Timber-frame construction. The Arizonia Elm is one of the densest wood I have ever dealt with, but machines good on a lathe, which means it lends itself. Minimal shrinkage and minimal checking on the specimines I have dealt with. It also splits well with a Fro and would make good pins. Strong and stringy. Doesn't break apart when snapped. Must be twisted and torn or sawn/cut. If your southern elm is anything like that, I'd say "Go for it."
Keith in Houston
