67 gmc leaf rear interchange?

[Renegadevtwin]

Just bought a 67 GMC 2wd shorty.
Has dana 44 open diff.
Want 10 or 12 bolt Posi
From what I have researched the previous generation C10 interchange.
Do the square body or newer interchange?
What years had factory 12 bolts?
Are the 12 bolts the same, internally, that came in the muscle cars of my past?
Thanks in advance

[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.