Early Barracuda "Heavy Duty" Rear Seat Backs?

First a question: Are the rear seats all the same 64-66 Barracuda? Thank you.

Is the factory rear seat back fairly heavy (weight-wise) or am I just losing muscle tone in my old age? Carrying that thing around it's quite a chore for me these days. I read somewhere that old seats can become heavier with age as the foam "absorbs" who knows what. Thank you.

rear seat 1.JPG

rear seat 2.JPG