Just a note, if replacing with a v/8 flexplate you must use a PRE-'86 (2 piece seal,internal balance type). The early cranks used 7/16 x20 NF threads,also measure the old flexplate diameter and replace with the same or you will need to change starter. 153 tooth is 12.85 dia.-168 tooth is 14.13 dia.
www.jegs.com has both sizes in the Jegs street version, also use NEW flexplate bolts, they are a special design. The 24/7 Tech person can help if you decide to go that way, with the above information. The local GM parts should carry the bolts.
