[70 copo]

Simple! From the memo:

"effective August 1st 1969, at the manufacturing plant all engines built per this deviation will be identified with a "C" preceeding the engine suffix..."

The start of the '70 model year is when the three letter stamping for engine identification was used.

These engines were carryover to the '70 model year production and were identifed as such.

Second generation production started up at the plants in January '70

Phil