I was mistaken on the non HO 68. It is a 01A chassis build with a 1/8/68 invoice.

As follows, the dates. L067 block, heads both L267, INTAKE L067, carb 3407, 7L14 distributor, exhaust manifolds L087 and L117, trans is P8T17 (December 17th), rear is a 3.36 nodular with a 255 date which is Sept 12th 67.

As I stated prior...the POSI N rears/heavy duty were 3.36 and up and will have a casting date much earlier than the other date coded parts. Standard rears will generally be closer to engine build. As an example, my HO has a standard 3.55 non post rear. Its date is L157 which aligns with all other engine/trans date codes which are all within 2 weeks. If I remember correctly, HD rears have a 3 digit calender date code whereas all others are the four character month/day/day/ last digit year.

As asked prior...engine components for 68 were manufactured in 67 as the model year was august to july. So, Firebirds with chassis build dates in 68...even into Jan can have 67 dated parts. There was no carryover of blocks (different casting number, heads, different casting number distributors (different casting numbers) carbs (different casting numbers.

A tidbit of insider info from my uncle who worked at GM for 42 years...with the latter part at the Willow run warehouse...was that whatever heads, blocks, intakes, distributors rears that were left over from a model year were warehouse and were NOT stamped with an EUN nor block code or VIN. These were for warranty purposes and or NOS purchase by enthusiasts.

Another tidbit...I was fortunate to meet workers from the Lordstown and Norwood plant 2 years ago. I spent the weekend there as a guest (and room mate) of Scott Settlemire (aka FBodfather) I got some really cool period correct 67-69 Firebird memorabilia from the workers. After a weekend...I got to talk to 20 to 30 line workers. A great percentage of them took GREAT pride picking individual dated components while the Birds were going down the line. Imagine men and women having a mid December 68 block trying to hunt down head and intake dates as close as possible to the rest of the drivetrain! It was also related that a small percentage of workers didn't give much detail to this endeavor of pride.

I will always cherish those discussions...they knew I was a purist and answered all my questions with pride!