I believe the knob will just change out, but but the late 60,s darts had their back-up or neutral safety switch on the shifter bracket (I can't remember which one it is for sure).
Hopefully somebody else will chime in and let us know for sure.
Nice original Exhaust Manifold Shield for small block. Nice item if you are looking for the original look.
Asking $20.00 plus shipping from Saskatoon SK, Canada.
Used power steering set up with saginaw pump and brackets pulled from a 72 340 demon.
Asking $100.00 plus shipping or Best offer from Saskatoon SK. Canada