I know it sounds crazy but at some point someone had info that 66 Canadian full size Chev and Pontiacs built in 1966 had K66. It seems like way too many "66's" to be believeable but supposedly there was documentation to prove it.
I'm not even sure how many years it was offered in Canada. I know one parts book I looked in (Canadian) listed it as being only a 1966 option.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)