Chuck,
"or if they are in fact two different styles of exhaust pipes."
I did a short search in The Albatros Publications Fokker Anthology Volume 1 and also the original Data File # 9, I may have a partial answer for you on the exhaust question.
Page 20 of the latter has a clear close up photo of the first albatross built Early D.VII 527/18 WN 5148 with a single exhaust pipe opening for the dual exhaust pipes. The former reference states that the 300 Fokker built Early D.VII's of the first production batch 227 - 526/18 had the "Dual Exhaust, center of cowling". These in any photos in either book have the double openings on their exhaust pipes. I seems that there were obviously these two different styles of manifolds with the single one being on the Albatros built machines. I guess which manifold to do would be related to the Serial or Werke number of your subject.
Hope this is of some help.
Cheers,
Lance