Other thing to look for is the date code. If memory serves, it's near the mount point for the oil filter adapter. First digit is the year in the 1960s. Letter indicates month - A for January, B for Feb, and so on. Last two digits are day of month. You can get your cars scheduled build date off the dataplate on the door (something like 16D for April 16). Look for a block a bit earlier than that if you want to really fine tune it. Depends on what's available, of course. My April 428CJ car had December head castings. Service block at this point, and I can't remember the date on the original. You can go nuts with this stuff. Intake is the easy one to look at date on. Heads are under valve cover, and block is down low behind stuff. Other than that, check the bore to make sure it's a 390 and not a 352 - most of 'em have 352 on the front of the block.