[buster73]

The shown reinforcement plates certainly make sense. Would be interesting to know if they were introduced because the notching of the tubes will make them somewhat more prone to bending by loads induced by the trailing arms in the longitudinal direction of the car. Should run the numbers through a computer one day. Could of course be coincidence and they were just introduced to compensate for better/wider tires, better brakes and overall higher performance. Anyway I guess a good modification for any early car if someone is welding the tub.