Not sure how many 7.5 rear ends you have see or worked on. Most of the 7,5 are 26 spline units those, include the G bodys and early S-10s. Some time after 88 or 90 the S-10 got the 28 spline units and all the G bodys had the 26s.

 

I've never seen a 26 spline 10 bolt 7.5. Oldest I worked on was one from an 83 Firebird and those axles were 28 spline. G-body might have had them, but I know all F-body were 28 spline and every small GM truck I've ever down bearings in was 28 spline.

 

You might want to spend a little more time looking up the specks on the GM 7.5. You may have found a upgraded rear end on the 83 firebird and you may only have looked at or worked on the later S-10 trucks. But yes all the early 7.5 came with the 26 spline axels.

 

1982-1989 cars had 10-bolts with 26-spline axle shafts. Starting in 1989 GM started the changeover to 28- spline axle shafts and this was not 100% until model year 1992. So there is a mix of later year cars with 10-bolts having 26 & 28 axle shafts.

 

That was my finding also. I know in my GMC full size truck with the 8.5 the change came in 1988 when they went to the 30 spline axels. I beat the snot out of it every weekend running brackets at the track. I used a 30 spline posi out of a cop car that came with the HD rear ends with the 5 on 5 bolt pattern.