April 25th was a Sunday in 1965 -unlikely (but possible depending on production need). Nearly all small blocks through 1967 were machined with 2.30 inch main journals. 1967 HP 350 blocks and all 68 and later small blocks had 2.45 inch main journals.

So - if you have a small journal, it's probably a 1966 327. If you have large journal, it's a probably a 1969 350.

Can I ask what you're planning to do with this engine and why the manufacture date is so important? As tech said - it's a 4.00" block.