Need lot of driveshaft & 8.75" rear end help


Interesting chart...

I've got a Scamp and I'm still wondering what length my driveshaft needs to be shortened to for the 8 1/4 that's going in soon. It has a 904 & 7 1/4 now soon to be a 904 & 8 1/4.

Why does it list two different length drive shafts for the same car (Duster, Dart Sport), rear end (8 1/4) and transmission (904):

3467151 1973-76 3.25 49.90 904/833 8-1/4 225 318 340 360 Duster Dart Sport

2996137 1973-76 3.25 51.89 904/833/230 8-1/4 225 318 340 360 Duster Dart Sport

Why is one listed as almost 2" longer then the other for the same vehicle??