replacing the whole quarter is not easy and will still require some filler when you are done because most aftermarket quarters are not as good of quality as the original metal.
Welcome to the Gold Duster Salvation Society. My first car was a 1973 Gold Duster. I have another one already thru paint and waiting to be put back together now. It is a /6 automatic and is being restored to full Gold Duster trim.
I had to replace quite a bit of metal. I have to check with my shop, but I think I still have both a brand new right and left rear quarter patch (not the full quarter panels). They are Goodmark, so as stated above they will need to be straightened. I haven't posted my un-needed stuff for sale yet, but if you end up posting a 'wanted' I will likely reply.