I'd ask the question on several sites as to exactly when NHRA began to allow 10-bolt GM cars to run 12-bolt GM rear ends.
Here's a response I got:
"...The rule as printed in 1981 reads..."Original rearend may be replaced with another from same automobile manufacturer. Distance between backing plates may not be changed. Any gear ratio may be used that fits third member case or housing. Limited slip or ratchet-type rearends are accepted. Locked rearends not permitted. Reinforcement of spring perch permitted. Spools permitted only with aftermarket axles."..."
So, if that was the 1st year that rule was in effect, then the answer to my question is 1981.
Does anybody here have a copy of a 1980 NHRA rule book, to see if the rule applied then, also ?
I ASSUME that before this rule went into effect, the only A or F-body Pontiacs allowed a 12-bolt were the 1970 models that came with a 12-bolt.