Seat belts in Commuter Two-Door Wagon
 

Hi,
I'm doing some fact checking for a novel I'm working on and I and need to find out the history of seat belts in Mercury's Commuter two-door station wagon.

I know that law mandated that seat belts be included in new cars in the 60's but I need to know what year (if at all) before then they were standard in the Mercury Commuter wagons.

Thanks for your help.