There was a federal requirement (from Aug/Sep '68) that the engine be 'uniquely identified, and VIN stamping is most expedient at time of installation , but there was no federal requirement on where it was stamped.
The issue of *where* the VIN was stamped on '69 engines, and the 'inconsistency' in location thru the year, makes me think that Chevrolet engineering management to address the requirement wrote specifications allowing for either location to be stamped (so long as ONE of them was); the LA and Norwood plants apparently chose different locations to meet this requirement.
It was probably faster/easier to stamp the engine low on the side, immediately before or after the transmission was stamped. It's obviously easier to rear on the pad! It may have varied with the person being tasked with that job, or possibly whether the engine was 'dressed out' with alternator/etc, or not, at the stamping time.
