64 Dart Gt 4 speed won’t shift into gear ??

On the right...look at the wire diameter, coil diameter, & number of coils. Smaller wire, larger & more coils = less stiff....larger wire, smaller & fewer coils = more stiff.
You might have to cut half of the exaggerated "U" hook off of the right one to get it attached, good pair pair of side cutters gets it done.
So you recommen I should use the thinker one ?