Rear Vinyl Trim Removal

Same trim, don't know when they changed fasteners - with your luck probably mid year 73...
You can reach above the wheel well in the trunk and feel the back of that sheet metal - if you hit pointy things - that's the end of the screw tip. The posts are welded in place so you can probably find the weld. If you are flexible enough, crawl in the trunk, shine a light up there and you should be able to see the end of the screw or the weld spots.