The carbs are found in two forms, one produced prior to 1976, one produced after 1976. Examples of each form are as follows:

Produced 1976 or later
17080243
2629 CNO

170 - Prefix Code
    8 - Decade Produced
          5 - 1976-1979 (1705)
          8 - 1980's (1708)
    0 - Year Produced
2 - Model
     0 - Monojet (1 bbl) Federal standards
     1 - Two jet (2 bbl) Federal standards
     2 - Quadrajet (4 bbl) Federal standards
     3 - Monojet (1 bbl) California standards
     4 - Two jet (2 bbl) California standards
     5 - Quadrajet (4 bbl) California standards
     6 - VariJet (2 bbl) Fed
4 - Division.
     0, 1, and 2 all indicate Chevrolet.
     4 - Buick
     5 - Olds
     6,7 - Pontiac
3 - Transmission
     Even numbers - Automatic Transmission
     Odd numbers - Manual Transmission
CNO - Customer Code
2629 - Date Code
  262 - 262nd day of the year
      9 - Year

Pre-76
7028219
DG 1938

70 - Prefix code. "70" will appear on all late '60's Rochester Carburetors.
      2 - Decade produced.
          2 - 1960's
          3 - 1060's with A.I.R.
          4 - 1970-1975
8 - Year produced. 8 = 1968
2 - Model
     0 - Monojet (1 bbl) Federal standards
     1 - Two jet (2 bbl) Federal standards
     2 - Quadrajet (4 bbl) Federal standards
     3 - Monojet (1 bbl) California standards
     4 - Two jet (2 bbl) California standards
     5 - Quadrajet (4 bbl) California standards
     6 - VariJet (2 bbl) Fed
1 - Division.
     0, 1, and 2 all indicate Chevrolet.
     4 - Buick
     5 - Olds
     6,7 - Pontiac
9 - Transmission
     Even numbers - Automatic Transmission
     Odd numbers - Manual Transmission
DG - Customer code.
1938 - Date Code
     193 - 193 rd Day of the year
     8 - Year