My '76 2wd Blazer has a 12 bolt but is 5 lug. The 12 Bolt rearends use a 30 spline axle vs. a 28 spline axle in the 10 bolts ('87 and older). The '88 up rearends use a 30 spline axle, but the spring perches and shock mounts are in different places. But, I can tell you that the rearend out of my '76 and the original rearend out of my old '87 will easily interchange as far as spring width and shock mounts. But I am answering from a 2wd world
Even the 10 bolt 4x4 pre '88 are still 28 spline, so you could just swap your axles into a 2wd rear, but I would be curious as to whether the spring perch is oriented at the same angle as the 4wd.