69 307 engine block ID question

[69RedCST]

Hi All , I âm currently restoring a 1969 CST Blazer. It had a 307 engine originally. I am looking for a 307 engine block that came out of a 69 Blazer or one that would not show any difference of one that came out of an 69 Blazer. I want to make sure the casting numbers or whatever would show that it could be the same as one that was in it originally. I understand that the serial number would not match . I’m not very knowledgeable about how this stuff works. Can someone direct me on a 2nd grade level. And if there is any for sale. I will buy immediately. Thank you for your time and patience in advance.