Here are some guesses at the codes:
F112L
F = Flint, MI manufacturing plant
1 = January
12 = 12th day
L = installed in a 6000 series truck
CON4 A78
A = January
7 = 7th day
8 = 1958
There might be different interpretation s of the above codes - people will post corrections, etc.
We will be able to tell you more,
if you post a few more codes from the head and block. 
