Block Stampings

[gbaker@customcpu.com (Baker, G.)]

To Those Who Know All,
  On inspecting the block of my 56 A I notice stampings on the panside of 
                                  " 7
                                   67
                                   60"
Also saw stampings of "GG".
Does anyone know what they refer to and if they are indeed factory stampings?
There are also two allen head plugs of different sizes in the block panside
surface.  Are they oil galley plugs or what?
I ain't got a clue as to the numbers.
Thanks for the responses.
Gregg Baker