I have a question about how they made this shotgun
lighter than the standard 12 ga. 1960 model.

I am looking for a shorter stock for mine.

They reduced the rib width they milled the receiver,barrel ring and the stock is dimensioned a little differently. I also believe the wood they used was lighter. My buddy had one purchased new in the 70's and the wood was nicer then the heavier ~A5's sold at the time.