64 dart shock upgrade

Nope. Bad idea, just like air shocks to raise the ride height.

The shock mounts aren’t designed to carry spring load. If you need stiffer springs, install stiffer springs.
And the coils will grab the fuel tank lip when going over bumps. (don't ask me how I know.) I peeled the tank out of my 65 Dart when bouncing over rough train tracks. It was on the highway and there was no fire but scary as hell! Back in about 70'