73 Plymouth duster ignition

yes, proper grounds are crucial to these old cars
check and clean the battery terminals, and make sure you have a good ground to the engine as well

then I would grab a screwdriver and try to jump it like 70aarcuda mentioned
just lay it right cross the two posts on the starter and it should engage

just be carefull the car is in park when you do so

that will tell you if the power is there to crank it, and if the starter itself if good