BRAKE DRUM QUESTION

It all depends on how you go about changing the bolt pattern.
If you just redrill the stock axles, you need to redrill the stock drums, too. There's no 5x4.5 drum that will match your backing plates and have the correct center register.
4"to 41/2 what backing plates
If you are ordering aftermarket axles with the standard Mopar flange offset (not the A body offset), then any mid or full size Chrysler, some trucks and vans will have what you need, but you MUST use the matched backing plates. Period. There are no 5x4.5 drums that work with A body backing plates.
What rear drums for 4.5" axle swap