1970 Chevelle LS6 Convertible

[bergy]

Ls9 Ragtop is, of course, correct. The casting date grid is divided into 12 "boxes" which are created by 5 vertical lines and one horizontal line. The top 6 boxes represent January through June and the bottom 6 are July through December. At the beginning of each week during the production year, a pattern maker would strike the die (these are permanent mold castings) with an additional punch mark in the appropriate month's box. So, 3 punch marks in the March box = 3rd week of March. It's important to remember that casting inventory wasn't controlled on a "first in - first out" basis, so a delay of up to 6 months from casting date to assembly date is permissible. Different permanent mold facilities used different style grids, but usually the same "punch" method was used to designate succeeding months.

IMO - The engine stamp appears acid aged - the depth of pitting is severe and pretty selective.