Just got off the phone with Jeff. Only 4557 GG he has is a December carb. Interestingly wrt what Sully said, March is the latest date that Jeff has seen. I know he has seen a few Ls6s in his day. He also stated that he has seen carbs as early as December on a June built LS6. So, I guess my search is over and I will stay with my late January date. Due to lower production numbers for certain LS6 components, Jeff says he sees this sort of thing quite frequently.
Thanks for all of the input.
Call Jeff if you need a December carb.