NASCAR tracks and the early 409
According to Terry Boyce's monograph "Chevy Super Sports 1961-1976" (page 13) "Rex White introduced the 409 to the NASCAR tracks with one of the 360-hp fire-breathers in his 1961 Bel Air Sport Coupe" (picture included on same page).
Of course, there was Dyno Don Nicholson (Roy's buddy
at Pomona tearing up the 1961 NHRA Winternationals (one of the first 409s on the West Coast?).
Dan Gurney also ran the 409 with the 369 HP in a somewhat stock Impala at the Silverstone International Trophy Race in merry old England. This was a production sedan race, and I think he ran against Jaguars and such.
Then there was Louis Unser and those Pike's Peak hill climbs (was it an SS or a Bel Air?)...
Boyce's book also mentions Ned Jarett form North Carolina winning the Grand National Champion (NASCAR) in a 409 car. Durability was the key issue here, as he was "consistently near the top during the entire season" (Boyce, p. 12).
Hope this helps some. I bet there are other factual stories out there as well.
Cheers,
Tom K