Tire size = 90/90-21

Is there a difference in ply rating between the regular K60 and the K60 Scout in this size? I believe this is the only size in which Heidenau still makes both flavors of tire, and in this size if one orders a tube-type tire (for early airhead G /S) then what ships is the regular K60 (Enduro). If one orders tubeless then the K60 Scout is what ships. There is definitely a difference in tread pattern but I don't know if there is a difference in ply rating and sidewall construction. Anyone know for sure?