64 Fairlane Light Weight was/is allowed fiberglass fenders and hood. Bumpers may be aluminum. They tried fiberglass bumpers and NHRA nixed that. From the 2021 book a 427 HiRise with stock heads and manual trans has a SS hp rating of 466 and a weight of 3206. That works out to a 6.87 lbs/hp. By a 1969 book, that would be just shy of the min 7.00 for SS/D and could be made up with weight. The bracket was 7.00-7.49. 1964's were the oldest cars allowed in SS in 1969.
My references are the current book and this site for the 1969 book:
http://www.superstockamx.com/page82.php