You can also do the same thing for the front of the frame and underhood braces if you got time on your hands, or you can go to the junkyard and grab them off a grand prix (underhood) or cutlass. I've seen the GPs with both style braces.
Home Depot, three quarter inch EMT and hardware. Made rear seat, front lowers, and upper fender supports all for about $25. Took a day or so but really tighterned up my t-top car.