I had the same problem with my hood. Repro springs, hood still sagged, then I bought repro hinges, hood still sagged.

Solution : Order a pair of hood springs for a 1979-1981 Trans Am. They're about 1 inch shorter in overall length than the 67-69 springs, and the same wire diameter. After 10 years now, and constantly opening and closing my hood, my hood still stays up perfectly.