I think this is Castle.  The Grand National cars are even worse than the the Trans-Am cars when it comes to identical numbers and paint-jobs.  There was another #17 identical to this one driven by Doug Schultz, or by Castle.  Which was which?  I have no idea.   Schultz finished 11th, Castle 13th, so the twin cars were near each other on the track as well.

And -- there was a 3rd 1968 Ford Torino, #17 driven by David Hankin, which was a non-starter so maybe it's not a candidate.