What is the differance between the sweptback and the stander drive, and are they any good?.

Mainly the case. The internals are pretty much the same as the standard cases. Depends on what model you are looking at.. B1, XR/XZ are about the same from old style to new style. Shiming for pinion depth is different on the newer cases, but that can be applied to the older ones also..

Hope that helps.
Dick

Is there an advantage to the sweptback design (i.e. does it act like a short extension box)?

Dan