[Mr70]

My Oct.69 built L-78 Chevelle has a Sept. dated 4492,without a two letter GR suffix.I believe there was some production confusion on the deletion of the suffix on the early assembled carbs.,be it over the counter or assembly line installed.
You should use the vehicles Cowl tag date for a Carb. reference point,and not precede it.
I've yet to see any 1970 L-78 Chevelle with a suffix on it's carb,regardless of plant,because they were only produced in the first 100 days of production.
The 6 assembly plants building the LS-6 Chevelle have shown suffixes appearing on their Carbs. as early as Dec.69,probably because the LS-6 was produced later.