I have two- one is the correct 1968 in the box, and the other is ~1970, but haven't had a chance to listen to them since my car is not done. They were GM promo tapes that came free with the 8-track. They are rare- particularly for pre-1970, but they come up on ebay every once in a while. I paid $1200 for mine, but I'd be willing to let it go for $900 to the right person.
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John
68 400HO Conv, HD3sp(now M20 4 speed), 3.36 posi,PS,PB,Rally II, 8 Track, Deluxe Parchment/ Flambeau Burgandy