I haven't heard of any reports of it being done at Tufts, so I don't know their success rate. I thought I had read that the University of TN had the best record for no seizures after surgery which is directly related to death from surgery. It would be my first choice if my dog needed LS surgery and that is taking into considerationt that we have Michigan State University here. My second choice would be Cornell. Now any vet school could've easily moved up past UT in success rate without me knowing, so you might want to call and talk to each school about it.
If there is no diagnosis yet, maybe you don't even have to worry about this part of it. It could still be MVD...
From what I have read, it is safer to go ahead with the surgery in a young dog with an extrahepatic shunt. Medical management is second best. Those complications are very real though.
I'm sorry you have to deal with this.