Hi Chris! Good question, Mike is correct,
The balck seat doesn’t have original , I just bought the screws and the washers in my town ( like a home depo ) . My blue seat has the originals, but the washer was plated , I like gold finish but it is not the original finish.
Here is an answer, you can see originals . The two really bad shape early seats have a silver screw and a silver washer. The detail can tell you they are not obtainable nowadays, the shape of the head of the screw is something different, and the washer looks a little bit thicker than currently available at a home depo .
And in March or April 1971 ? A set of new seat belts and hook were applied,I guess that time was a change of the seat too , the seat bottom would have lost the guards and , the seat back lost the hook which transferred to the body side interior trim .
And I assume the change of the seat back would be made at this point , “ fat seat back “ replaced by “ narrow ( slim ) seat back “ .
It is going to be interesting that everyone look into the seat bottom frame , if you find the holes for the guard , is it March or April 1971 or later ?
By the way , an early seat back has a hole for the seat belt hook , the hole can be seen both side right and left for the efficiency of the production. I will check my seat bottom frame if it has holes for the guard both left and right.
Kats