[Mike C]

Truck 12 bolts are not the same as car 12 bolts. 12 bolts came in 1/2 ton trucks exclusively until about ‘79 when they were interspersed with 10 bolts until about ‘82 when the went exclusively to 10 bolts. A 10 bolt from a Suburban or Blazer ‘88 and newer should have 30 spline axle shafts like the 12 bolt while 10 bolts from ‘79-‘87 will be 28 spline. There are different widths on axle housings as well. 67-69 are one width while 70-72 are another with possibly some of each in 1970. 67-70 are 6 lug and 71 and newer are 5 lug in two wheel drive but 6 lug still in 4 wheel drive.

2 wheel drive trucks both 67-72 and 73-87 should all have 42.5” spring centers but newer housings would require shock relocation. 67-68 GMC trucks seem to have the Dana axle as stock while the Chevy’s were 12 bolts. Not sure why this was but it is.

Why not just put a limited slip in your existing Dana 44? They have an 8.5” ring gear, should be 30 spline axles, and unlike the GM axles they use positive axle retention and not C-clips. Unless you want to convert to 5 lug axles (which I did on my ‘69 as they have better wheel selection). But if you are planning high performance use, adding the limited slip and buying new 5 lug axles for your 44 may be the way to go because of the lack of C-clips.

Note that you cannot use later model 6 lug wheels on an earlier truck because the hub bore is too small.