[70rs]

Sure you could build it. There is A LOT of sheet metal that will have to be changed. Including both quarters and the roof. And some internal structure around the back window. That is if you want to duplicate the 70-74 rear window. The tail light panel, lower rear panel, fenders, hood....pretty much everything but the door skins. And even those might be a little different at the handle pockets. But depending on how close you want to get from a visiual standpoint you could do it with much less than I just listed. (I think the blue camaro in your picture is a 75. Unless there was a mid year change to a bigger back window in 74. As far as I know the 74 models still had the small back window but got the big bumpers on them and new tail lights)

If you want to duplicate the look of a 75 and later you can keep the rear window, quarters, roof and not have to change the inner structure at the sides of the back window. Just swap out the fenders,hood, nose, rear panels and interior and you will have the LOOK you want.
Going for the '75 and later look will help keep costs down. But if you want the small back window of the early design you can do it. I like the early second gens (both Camaro and TA/'bird) better myself. Have you tried finding a 70-73 body(even just a shell) and then use the car in the picture as a donor?
The picture is of a 1974 GM promo ad. It shows the back window and it is the small one just like 70-73. The 74's are pretty cheap if you can find one and it would save a ton of money in metal swapping.