Okay I checked my TX-Sector manual and my 1986-1992 Gottlieb parts catalogue and there is no reference to the locking bar.
In the parts manual and the respective game manual, it only signifys the headbox as a whole with the individual translite, speaker panel as having unique part numbers. Nothing to the degree of what is missing from your Big House machine. The 'cabinet assembly' of which I presume the part in question was in attached to, was the only thing mentioned.
Best thing would be to email Steve at PBR or find another machine with similar locking properties and fabricate something from there.
