ZL1 engine

[GMH454]

When it comes back check those numbers and let us know. Also inside the block, look for small stampimgs. Did you get the caps ??????
Does not sound like it was cast by Yenko,who took over the tooling. Not sure why you don't have a date. Believe all 1969 cast blocks had date codes but will be happily be corrected.
Presume you have checked the front stamp pad. Is there even a trace of a number ????
Did it have liners. Does it have studs.(and caps ) What bore will it be, very lucky to find one standard bore.All these attributes effect value.