On my 69 coupe the bottom cushion (across the front edge) measures 53" inches, and the back cushion (across the top) measures 43 ½" inches. This is width from left to right. I did not measure the material going down against the quarter trim panel, just to it.
The height for the back cushion is 30" inches. This is from where the material starts on the bottom around the frontside and over the top. I measured the middle of a seat not at the center hump.
The bottom cushion measures 27" inches. I measured it as I did the upper cushion.
Hope this helps