Couple of quick questions.

Do I just have to pull off the diff cover to count the axle splines or do I have to pull out the axle shafts?

I have an 89 and in most of the posts I've read they say that 89 was the changeover year from the 26 to the 28 spline axle. However I've seen a couple that say that 88 was the changeover year. What year was it?

 

You have to see them (splines) to count them,whichever way you want to do it. And 1989 was the changeover year on the 10-bolts.

 

Chances are your 89 is 26 spline. There were not a lot of 1989 28 splines. There is a slim possibility but don't expect it. By 1990 they were all 28 spine.

You won't be able to count the splines with just the diff cover off but you need to pull the cover off to get the axles out anyway.