I just finished installing a mid-80"s Blazer 4WD rear axle in my 52 GMC. The old axle measured from the center of the axle to center of the axle, 63 7/16". The new axle measured the same way was 64 9/16". 1 1/8" wider for the new axle. That is only 9/16" for each side.
The new axle is a 3:08 ratio which did slow down the acceleration a bunch, but now I can run 65MPH at 2000RPM. The new axle is also uses a 6-bolt wheel pattern and I am running the stock 16" wheels.
You can check out my write up of the swap along with a few pictures at the discussion board of oldgmctrucks.com under the grease pit category. Or use the following link to go directly to the post.
http://oldgmctrucks.infopop.cc/eve/ubb.x?a=tpc&s=272004236&f=294006236&m=636107195
