Is it possible to convert??

The shock mounted overload springs are a little hard on shock bushings tho. And there's not much room between the shock body and the tank. I have used them back in the day, on both a 70Dart and a 73 Dart. Both times I had to bend the lip on the fuel tank to make room. Also, eventually the coil springs rubbed on the shock-body and made a very annoying racket back there.
New or different leaf-springs is a much better solution.