As far as I know, all of the OE 8 3/4 3rd members have the same spline count. Now, if it was an aftermarket set up for drag racing it might be different. But I've never seen anything that said to even check the number of splines on an OE 8 3/4 3rd member to see if the spline count was the same as the OE one it was being swapped with.
This is correct. I've taken several 8-3/4's apart all the way from an early 60's unit to early 70's units (open's and sure-grips) and they all had 30 spline axles. Only aftermarket stuff is different.
