The second one?
Probably a Wood Brothers prepared Ford Galaxie at Riverside in the Motor Trend 500. I'll further guess it was 1966, the fourth of his four consecutive (and five total) races at the road course, which was informally dubbed the Gurney 500.
He broke his string losing to Parnelli Jones in 1967 after being docked a lap in what some consider a bogus penalty for a minor infraction, but came back to win again in 1968
Note that these were full 500 mile races, about half again as long as a typical F1 race and Gurney's endurance driving experience (he carried AJ Foyt to a Lemans win in 1967) no doubt contributed to his successs.
Here's a way to win a bar bet. Who has the best winning percentage in Nascar history? Not Richard Petty or David Pearson or Dale Earnhardt or Jeff Gordon. That would be Dan Gurney with five wins in 17 total starts.
And while Gurney never won a world championship one could argue that he's the second best Amercian F1 driver (behind Eddie Chee..Mario Andretti)
At Jim Clark's funeral, Clark's father took Gurney aside and told him that he was the only driver his son ever feared on the track.

Or I could be completely wrong and it could be Buckshot Jones, at the Napa Auto Parts 500.

allen