lol I used to fall asleep up on the package tray.
I would not take my newest addition in the 67 till he is over 1 year old. But my 12, and 5 year olds I had no problems in taking when the car was on the road. Even when it wasn't necessarily road worthy...., but I live and drive on county roads except for the mountain I live on and drive down to get to the roads.
I used to sleep on the package tray too.
I think that having little ones less than about a year old is probably not the best idea either.
I would have no problem letting older kids ride in my Mustang though.