Hi-
I had the same problem with the retracting on my 73 Swinger. I found a solution...a temporary one, at least.
Reach under the plastic piece that hides the rolled up seatbelt, so your hand is between the floor and the roll of seat belt...the plastic cover does not cover this bottom part so you can reach up in there a bit. You will feel a small flat piece of metal/plastic that sort of covers over the rolled up belt. This must be part of the retraction system. If you push up on it, toward the roof of the car, the seat belt will be released.
I found that the retraction wasn't working right because there was twist in the belt. The twist was way down at the end so it never go pulled out and so never got untwisted. If you press the release piece under there, you can pull the belt all the way and then let it retract perfectly...that might fix your problem. It did for me.
Good luck.
Charlie
