Sorry to jump in... I specifically registered on Club Cobra today only because I found this post and am personally interested...
I think I can confirm this is CSX2171, not CSX2191. Besides what I found
here (showing closeups of the same Utah license plate), my father happens to be a former owner of CSX2191. He owned CSX2191 circa 1967 through '72 or '73, I believe. I was born late '70, and have photos of myself with the car that are undated, but I appear to be around 2 yrs old. CSX2191 was blue at the time (Guardsman Blue, I think?). In the AC Cars chassis register CSX2171 is listed as "white red trim" and CSX2191 is listed as "bright blue black trim".
Having said that, I've always been on the lookout for CSX2191 (which is how I got here today!). Anyone who ever stumbles onto information on its current state is welcome to send me a note!
Thanks,
Bryan Jones