I have 70 exhaust manifolds 3909879 & 3916178 with K49 and K59 date codes. Are they October or November built, or should I say did they use "I" for a month code or not. Thanks.

Don't know if 70's were the same, but in 1969 "K" was November and "L" was December. Sounds like "I" was in fact used.

Yes, they used I, so you have November date codes.
Bruce

Were the Delco parts the only ones not to use the I's

Don't know if 70's were the same, but in 1969 "K" was November and "L" was December. Sounds like "I" was in fact used.

Thanks, just going through the El Camino, checking dates, seeing if anything had been replaced.