I got some new fan belts from Napa that were part #28454, but when I tried putting them on with the fan pulley loosened, the belts still wouldn't wrap around the accessory drive pulley. I gave them the old belt, that had no # on them to match up. Maybe they gave me the belts for a series II 310. The engine is a 855 small cam cummins in a 1977 model St310III.