The pad shape is right for a '69 and the casting number is right for a '69. The Flint plant assembly stamp is not right for a car. The implied assembly date of March 26th, 1969 would line up with the short time period this casting was used but the rest of the assembly stamp has too many digits as the "8" does not belong there and the 2 letter suffix does not match up with any typical car application. Casting date has not been shown yet but I would expect it to be around March something of '69. If there is a VIN derivative on the pad by the oil filter we might be able to pin it down but without that info, we are just spitballing in the dark.
If there is no VIN derivative there, this blocks original configuration will never be determined. No reason to worry about it. It would be just another engine block.