7 1/4 to 83/4 swap - A Body

Plenty of threads on this subject but here's a quick run down . You'll need the following .
Larger u bolts
8 3/4 " shock plates or modify The ones from your 7 1/4" to fit the larger u- bolts
Yes your d/s will need to be shortened
Install the axle get measurements and have a reputable shop build you a New d/s
Chrysler uses two size u joints determine which your differential has and have your d/s built with that size u- joints and yoke.
If this is an a-body axle the width should be the same .
and if the brakes are stock your wheels should be fine.
You don't state what cars are involved in this swap.
Therefore I am answering on the assumption that this is between two a body mopars all stock with SBP .