My engine (which was installed in '53 as a short block) had the last few digits of the casting number ground flat and restamped. Used to be 3835_4_ (probably 3835946 - built in '53), but the last 3 digits were stamped 794 which is a '42-'53 date range. It's located on the right front just above the pan mounting flange. But mine has no serial number behind the distributor, or evidence there ever was one. Must have been a GM replacement engine.
Is there evidence that your casting number was removed in that location?