There were actually two different C39-8 locomotives. The C39-8 classic was a classic pile of crap. The C39-8 E (enhanced) was a much better locomotive.
I don't know if there are external differences or not, I do know that the entrance to the main electrical cabinet on the classics was on the firemans side. I sent many C39 classics to the scrapyard. Unfortunately I wasn't able to save many of the E models either.....
I just saw an ex MMA C39-8 classic at truck and electric last month.
Randy