I have a 68 olds cutlass s. It has a single axle I need to know how many spleens it would have Any help would be grateful thanks

 

I'm assuming you are describing a "single wheel peel" (non-posi) rear end (not that it matters, because it doesn't).

If it is the original Type-O axle (12-bolt cover / 10-bolt 8.5" ring gear), it'll most likely have 28 spline axles. 31 spline axles were used with higher numerical ratios (4.xx+). If you check the axle code stamped on the passenger side tube (careful cleaning sometimes required to find it), you'll know what is in it if it hasn't been rebuilt / modified.