Removed Column Shifter, but how do I keep it from rotating?

I know Brewer's Performance carries the steering column collars for floor shift, at least for some models. I bought them from them for my Charger when I bought the conversion parts to go 4spd. Mine was a '69 though so no ignition in the column.

They might have what you need. Worth checking to see how their prices compare to Mancini.