Brought Dart to shop to fix idling issue and car runs like s**t!

Not trying to pile on with the shop you took it to, BUT a lot of shops today vs older more experienced shops.......its like comparing McD's vs The Keg. Finding a shop that KNOWS 60 year old cars is hard. Just because they are licensed doesnt mean squat. We as owners either have to invest time to learn(fabo) or be prepared to pay good $$ if we can even find a good shop.
I would think above advice will straighten out the issues. Have you put new Rhoads lifters in? I would think with proper timing, valve lash and new lifters that the problem is minimized/isolated?
Good luck!