Yep, I was just editting when you posted again. You're correct on the lengths of shafts being the same in 70 series and 40 series. I was incorrect and have fixed my post. :doh: :slap: (for me)
Also, I forgot to mention I second the motion that you should not get the downey kit. I called...
Sorry Joe, your post was almost perfect... :D For the FRONT you need the long side axle shaft to have long splines--it's the rear that would need a longer splined short side. This is because when you swing an 80 series REAR diff around to the front of a 40/55/60/whatever the actuator goes from...