I think I may have found some of the source of confusion. In the 1967 parts book they list two engine codes for the 273, "D" for "273 C.I.D." and "E" for "273 H/Perf. C.I.D." So it appears in '66 there is only one code and in '67 there are two. As per the parts books.
"We live in a time when intelligent people are being silenced so that stupid people won't be offended".
