I'd have to look it up but as far as I know the Shelby 1" drop was used by Shelby when Ken miles was testing a proto type mustang coupe around early 65 prior to Shelby building the 65 Mustangs, I know it was used in the 65 R-Models which was in 1965. I don't think it was used in 66 Shelby's much because for street Shelby's they were looking at cost cutting and getting them out the door. Also the last 252 65 Shelby were sold as 66 models and known as Carry-Over 65 Shelby's today and have there own special pricing. Dale M