When did 10 bolt change spline count?

[ciffer]

I am going to buy a limited slip for the front of my 88 suburban, I need to know if it is 28 or 30 spline.

It was built March of 1988.

Also, are front and rear parts interchangeable?

 

[4X4HIGH]

The 30 spline started in 1989 BUT I wouldn't count that as gold since GM has put "later model" stuff on the previous years before. You would be very wise to pull an axle first and double check what you actually have.