yes to swap axle from large to small you need the correct axles with the matching c-clips IIRC.

84 should be the 5 on 4.5 85 was the change.

spring pads should be 43" centers and bolt right in the truck.

if you are replacing a 10 bolt, it is smaller and may need a drive shaft correction.

9 1/4 to 9 1/4 is bolt in.