Gene's version is correct...thanks for jogging my memory!
Although many noted NASCAR authors agree that Chrysler's execs beefed so loudly to NASCAR's Bill France in late '64 that he listened and acted, the SOHC was not "banned". When the 1965 Rules were published in late '64, the Cammer was hit with a 427 pound weight penalty over the straight valve FE. Hence, the Rules effectively removed it from competition.
And yes, NHRA also bent over backwards in the day to accommodate the Chevys in early Pro Stock yet the Clevelands still did very well! Later, the Pro rules were changed almost weekly via weight breaks to level the playing field, yet still the 351C runners did end up on top most of the time until the 500CID rule was enacted.