Mine uses the same length belt, or rather, it did. I don't have smog now, but with or without u/d pulleys, the belt size is same. Somebody correct me if I'm wrong, but don't underdrive pulleys work on this principle?:
The alternator and waterpump pulleys are larger, causing them to spin slower. The crank pulley is smaller, to make it spin faster. I heard that once, it makes sense. So the smaller crank pulley would make up for the larger other pulleys. Isn't that how they work?
So happens I was able to use my stock belt and that's probably why there is no clear cut exact answer to what belt lenght you should use with just about any setup you running. On the tensioner it shows that I'm just about maxed out but I haven't ran into a problem "yet".