Hi.
Need this carb decoded.
It's a 4555 Holley Part# 3972121.
Build date is 2/27/4 (How does this break down?)
Thanks for your help.

The 4555 list # is for a 1970 Z-28 350/360 with 4-speed trans. The date appears to classify the carb as a replacement as most Holleys of the early 70's were dated in the year,month,week format, e.g. 032 would be 1970,March, 3rd week. Replacement carbs were generally Julian dated, e.g. 2274 would be 227th day of 1974, significantly later than the date of original application.