Had the ones on my kids 62 300 done.He had them add a leaf and 1 inch more arch at the time.He drove the car at least 14 years and they were better than any new spring you could buy now.He beat the car to death mileage and racing.My 57 if the mains werent all broke they would have been done also.Just happened that local spring shop had a set they made probally 30 years before that I bought.Rocky