71 4door dart full suspension help

You don't have to switch to a 5x4.5 when switching to disks. The cheapest way is doing the ScarBird conversation. With that said they is a complete factory KD set up for sale right now in the for sale section for a good price.

Sounds like your car is going to see about the same use as my dart. I personally figured I might as well spend a little more now and get some better upper and lower control arms from QA1 and a bigger torsion bar. But if you’re happy with how the car handles now and just want to freshen it up then a rebuild kit from the likes of Summit would work.