904 to A833 Neutral Safety Switch

On the 833 4 speed it is not a NSS. The switch is strictly a back up light switch. There is no NSS on a 4 speed car. Your 68 back up lights are wired to a switch either on the steering column (column shift) or the automatic floor shifter. You should be able to run that wire the the switch on the transmission.

Later (72 and later?) Cars had a clutch interlock switch on the pedal mechanism, but not in 68 I believe.