3 quick problems

There is more to removing the rear seat back. Early builds had 2 long sheet metal fingers poked through loops of the seats frame, then bent/folded left or right. The later models got actual bolts down there. Either/or, you'll need to release those before the seat back will lift off the upper hooks. Knee down hard enough in the seat bottom versus remove the seat bottom.

Really? My 70 just lifts off, I also had a 67 that was the same. Of course those bolts could have been missing, and I have no experience with a 71.