What will I need 6 to a 340 on a 66 Dart?

Thank you. Just got back here. Had to go home and take care of the pups. Vertebrae in neck and they want to operate. C4 5 6. No really good chooses here. Came on gradually over about 10 days. Hard, arm and fingers. O poop. They are keeping her a few days and I guess we’ll see if it gets better or worse and go from there.