A dark colored 1968 Camaro RS/SS Convertible was used as the pace car for the Labatt Indy 200 USAC National Championship Trail event held at Circuit Mont-Tremblant, Mont-Tremblant, Québec, Canada. Two separate 100 mile heats were run and both were won by Mario Andretti in his Hawk III/Ford. Heat #1 took place on Saturday, August 3, 1968 and Heat #2 happened on Sunday, August 4, 1968.
While I can't be 100% sure, this is probably the same car that was used to pace the Trans Am race held at the track the prior month. See photos of the car pacing the Trans Am race in this thread:
http://www.camaros.org/forum/index.php?topic=17566.0 In addition, it looks like they decided to keep the center caps on the Rally Wheels this time.
I found the picture at the Remembering Mont-Tremblant Facebook page. Thanks to CRG member Mike in Canada (group/7) for alerting me to the web site.