Have a friend that has restored a late model JD D.  He purchased it with the understanding that it had the rare factory dual exhaust.  He is starting to question that because the exhaust has no casting numbers.  Was that a factory option or was that always an aftermarket add on?  He stated that because of the dual exhaust the engine is supposed to gain 6 hsp., which would be significant for that low hsp tractor.  He is starting to have his doubts about the exhaust.