I have a dilema here,I've located a carb for my 70 Z28 but the date coding is four digit (2392,julian date) which translates to the 239th julian day or Aug,27 1972,eveything I have read indicates that this carb should have a 3-digit date code (year/month/week).
It has a GM part#3972121,& List-4555 above the date.Any help is greatly appreciated.

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1970 Z28/RS
Hugger Orange and in a million pieces.

Maybe the carb you have found is a repro from Holley??

70z,I think you have a replacement GM carb.you are right about the date,the 2 may stand for 72 or 82 [probably 72 though] most original cars I've parted have had the 3 digit date,year-month-week,My own 72'z'had carb replaced under warranty after 2 failed repair attempts in 73.I have all the paperwork regarding it and carb has 4 digit [3532,353'd day of 72 and correct PN.]date code.as to how long GM-holley made correct # replacements is a good Question.I have since procured a 3 digit numbered carb but which is more original? one that has sat on the engine since 73 or a unit from a swap meet????Anyone else have similar experience? later Steve!!

the 4555 carb is the right one for a 70 z-28 with a four speed. contact holley on the internet they will tell you where the date code is