The above picture has part number 3937930, which sounds like it was the early factory line correct part.
Here is a mount that listed both part numbers, 3937930 and 3920627. I also found some info from a previous post on the CRG forum that has engine mount, 3920627 with the engine stop bracket, 3977983.
There is a good post on the CRG site:
http://www.camaros.org/forum/index.php?topic=4961.0
One could conclude from this that when GM released a newer version (June) of the mount they placed both part number, original 3937930 and the revised number 3920627 on the mount, and when 3920627 mount was called out in the production run or ordered over the counter the new part number would reference the engine stop bracket 3977983.
Is my assumption correct??