Hey mate, as long as the person welding knows what they are doing it would just have to pass engineering. On the other hand, if you can modify your stock rails to fit, then it would either not need to pass engineering or pass engineering easy as.
John Wilson did my engineering for my car, so he is the man to look up and ask.
These seats are the bargain of a life time, I just need the money and garage space. The scratches could be gone over with a spray can.