Don't scrap the chassis. I would get my book out and go through the different rails, checking its dimensions, and correct them as I went along. 25mm box section is really cheap, it's nothing that can't be repaired with a little sun and a few cold beers ! If you leave these problems, you will have trouble with suspension alignment & cosmetically, you may struggle to get off the shelf bodywork to fit. On the weld side of things, if the builder has struggled to follow a build spec, I would have massive concerns about their welds. Every welder I have ever known knows how to measure. I would test the welds, and rectify any rubbish ones as I went along, your life depends on it !
