« Reply #22 on: May 28, 2020, 06:51:08 AM »
I had to go and look it up again, but here's the explanation on GM-produced parts, from the 'numbers decode' section. Presumably the same date coding was applied to externally-supplied components:
For cast-in date codes on GM-produced iron and aluminum castings (engine blocks, heads, intakes, water pumps, etc.), the letter "I" was used for September, and the last month of the calendar year (December) was the letter "L". For stamped-in date codes on GM-produced components (alternators, distributors, starters, etc.), the letter "I" was not used - "I" was skipped, and "J" became September, with December being "M".
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Tim in Australia.
1969 04A Van Nuys Z/28. Cortez Silver, Dark Blue interior, VE3, Z21, Z23, D55/U17, D80, flat hood.
Sold at Clippinger Chevrolet in Covina, CA.
AHRA Formula Stock at Lions Dragstrip, NHRA E/MP at Pomona Raceway