Help with rear axle spline
 

Ok, im looking at putting a 3:73 posi rear end in my car. Its an 85 TA with 7.5/ 10-bolt 3:23 limited slip rear end, but when looking for the posi unit, i realized i dont know weather i need 26 or 28 rear axle spline, and i really cant pull the rear end apart right now. So im hoping that there is someone out there who might know. Thanks in advance.