Nope, the holes are different. I originally had a double on my 69 and it got busted in a rollover. Last year I got a single and when I went to bolt it up, the holes were completely off. (Design engineers...you gotta love 'em)
I decided that fiberglass is easier to drill through then metal, so I'm using the original holes in the bedsides and I'm gonna weld in the nuts so I can easily remove the top without having to mess with the interior side panels for access. (I'm making new ones out of ABS plastic instead of plywood. Less chance of moisture problems)