Looking closely at this, I now think all they had to do was add a single bracket and new pulley in the location I noted to route the belt. I believe they have retained the stock tensioner in its original location. The tensioner and its pulley are immediately beneath the new pulley. If this is right, I think it's a very good (and fortunate) situation. The stock tensioner is spring loaded which keeps tension on the belt during high RPM. Looks really easy to install too. I would say with the use of the stock tensioner, going significantly smaller on the SC pulley would make a belt length change likelier.
