Originally Posted By DARTH V8R
Originally Posted By RapidRobert
Originally Posted By CMcAllister
I believe the "late" block began with 74. The casting numbers are different. Regardless, I wouldn't trust QC from the 70's and would have everything sonic checked for core shift, etc., before going crazy with one.
Agreed & I think the first number went from a (3) to a (4).

mine was cast 10/10/73.. 496 block. What do you mean 3 to a 4?
Ma changed the first number from a 3 to a 4 to denote the (so called) thin wall change which we now know from Andys work was hit or miss or something not the same across the board but there definitely was a change somewhere that was denoted by the first number changeing

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