Rather than just a total vehicle weight, do you have any dirt track circle burner friends who have a set of individual wheel weight scales?? These figures, the weight of the stock T-bird (should be available in a Chilton's book), and a freindly parts man with a good catalog and you should be able to get close on the correct weight spring. As light as an Effie is, the rear springs have got to be way too much. Hope this will help you.