It is actually easier to see in the picture than on the block. Lookin a little closer it is possibly L 7 6. That would make it December 7 1956. This would seem possible as engine came from a 1957 big Chevy truck.

1954 Chevy 1300 engine 235 (1959)
1955 (first series) Chevy 3100 engine 261 (1957)
1927 (other brand) Model T- engine 327 (1968)