Sorry if I might be wrong about this but why cant you use the originally installed column mounted N/S switch.
You still have the linkage running up to the column for the Ignition lock correct? So if you leave that linkage hooked to the trans stock location with cable attached for the floor shift, when selecting park, rev, nuet ,or drive the linkage still drives the internals of the column.
Or am I missing something unique to chevelles?
Its been along time since I did the swap there might be something I've forgotten
72 TPI El Camino
"Whaddya mean, no warranty?"