Mid seventies A body weight

so....where did they gain weight?
bumpers? did they have some safety steel in the doors etc?
bumpers, door bars etc. I know my 74 rear bumper weighed nearly 70 pounds WITHOUT the shock brackets, those added another 20-30. Mean while 70 dart bumper that I now have on the car weighs maybe 30-35 pounds WITH the 70 mounting brackets.