differential question
 

I saw an S10 at the junkyard with a disc brake differential. Are the diffs compatable between the Blazer and s10?

a full size blazer? no, a s10 is smaller, narrower.

They are between s10s and s10 blazers

If you seen a s10 with disks unless it was a crew cab somebody had swapped in a s-series blazer rear axle (or the brakes). S10s never came with disk brakes, suvs after 98 all had them.