Choosing a rear suspension

Verse springs @ $2-4 each which is incredibly expensive since Fiat took over and stopped making stuff. You could go to springs and things (espo.com) and pay about half.
1971 DODGE DART Stock Height Springs - Leaf Spring Type

And again some incredibly expensive Mopar parts which can be purchased a lot cheaper
1971 DODGE DART Mopar Performance Straight Shackle Kits P5249715


Your shock purchase price is on you but included with the “kits” above as well as the other parts.

You would reuse the front spring hangers.