68 Skylark reverse lamps dual filament?

Trying to trouble shoot the reverse lamps on my Skylark. Started with the bulbs and noticed that the bulb is dual filament. This seems odd to me and I am not sure if that is how it came from the factory, or someone replaced the sockets at some point. Anyone know if these are correct?
Neutral safety switch has been by-passed, for the neutral part anyway. Assuming the switch is bad since it exploded in my hands when I took it out, going to start there.
According to the Chassis Manual the back up lamp is an 1156 which is a single filament bulb. When you look into the socket, is there one or two contacts on the pigtail?
Chassis Manual is HERE.
Yes, two contacts, which is why I found it odd. Everything I saw also said single contact/filament bulb. The only advantage I see is the lights are brighter with two filaments? I have them working now, the neutral safety switch was the issue. It's also nice that the car only starts in park or neutral now :).
dual filament is not odd at all, possibly for your car, maybe. on a 63 the dual filament bulb has turn signal and driving light. power is provided for each circuit in the bulb and it grounds onto the chassis, lamp assembly. the OEM connector/bulb holder is black. if there is a white bulb holder, black and white wires, than it is the chinese crap that everyone is selling. the aftermarket white connector replacement the metal tabs are too soft and they slide out, so your lights dont work. you have to glue in so they dont come out and bend the tabs repeatedly.