All the calipers GM used on their D60's from 77 to 91 are exactly the same. They are even the same as the ones that came on 2wd 1 tons of the same vintage. Do your front hoses have a big square block on the caliper end that is interfering with the two little nubbies that stick up next to the banjo bolt hole? Thats the only possible explanation for the trouble you are having that I can wrap my mind around.