As per the other replies, what you’d like to attempt is a mammoth task! Even working with 2mm steel is a lot more difficult that shaping body panels at 1mm (or less). I, like seemingly everybody else on here, am up for a challenge but sometimes you need to be realistic about what you can achieve with the skills, equipment and time at your disposal. If tubular arms aren’t allowed, I’d think about adapting something; how far out are the road car items? Even then, it’s obviously a safety critical part so you’ll need to be sure it’s done properly.