No, the NEJ 120 does not supply Heading Hold mode.
In fact, even the successors like the Piezo 900 oder Piezo 2000 from
Graupner were "Normal Mode" gyros only.
The NEJ 120 was one of the last mechanical gyros (if not _the_ very last), so it really came with an electric motor, you could hear that one spin up and cause quite some noise, depending on the mounting plate and resonance..
No, unfortunately at least I don't have a manual available,
probably somebody else has one somewhere and would be willing to scan it.