The rat rod idea is not different from building anything. Safe or not is the question. The point being it is all up to the person building it. I have a mechanical engineering background and have built several harley-davidson choppers. The chopper world has brought about a lot of new parts to buy instead of making/fabricating the most important items like frames and front ends. With that said it is really easy to look at many car and cycle projects and become concerned about the structural integrity. Is this safe. Are you as the builder really have the talent, ability and understand the engineering to make an item in the correct way. I'm making a general statement about this. I remember in 1971 when living in Co. with a chopped extended front end. Co. had a state law on altered suspension. I was pulled over, ticketed and the cycle was impounded. If these custom car/cycle become a problem with accidents due to poor workmanship, then more laws of restrictive use will come about.