the track on the dana 60 front is wider than the 10.25 rear by 3 "
thw dana 50 ttb is the same width as the 10.25.
the main reason for the spacers is looks. In stock form the difference is not as noticable, but lift the truck 4" and put 35"s on the difference is noticable.
the other reason is the understeer caused by the different widths. I cant say that I noticed any difference one way or the other.
Back in the 90s there always were adds in the back of the magazines targeting the blazers to add wheel spacer to the rear, they were off 3 or 4 from front to rear. The reason the add stated was understeer.
as far as steel vrs aluminum, I sheared my axle bolts and no harm was done to the spacers