I actually already found out how to do it. Somewhere along it's 47 year life, one of its owners actually welded on some new seat racks so he could move his seat farther backwards. Must have been a tall guy! Anyway, he didn't drill through the new seat racks in the back like he should have but rather just bolted the seat down onto the rest of the metal sticking out (almost touching the backseat). I actually have some pictures of it as I was tearing apart the inside of my car so they will be up shortly.
And to my avail, both floor pans are in good shape! Neither have any rust holes or anything, just minor rust which should come off easily. I am the happiest kid alive right now.