I would check the pump timing if nothing else just to eliminate this from your list. The engine timing may be spot on but if the pump isn't firing at the correct moment this can cause the engine to run lumpy smoky etc.
You should always put a new belt on an engine that you don't have first hand knowledge off, every one will tell you that it's fine it had a new belt a couple of thousand miles ago just before I took the egine out!!!!