The correct information can be found in the "Restoration Guidelines & Judging Standards", Area 18. I have added photos of this information.
The 1928-1929 headlamp mounting bar is tubular and FLAT between the two headlamps.
The 1930-1931 headlamp mounting bars have an arch between the two headlamps.
The pressed steel bar with slots for mounting the license plate was introduced in May 1930 and discontinued in September 1930 when it reverted back to the tubular style.
All three styles of headlamp mounting bars are forgings from the fender up to the lamp mounts. There is a description and photo of the headlamp mounting bars on pages 18-2 and 18-3 of the "Model A Restoration Guidelines & Judging Standards", which is available from MARC and MAFCA and most major Model A parts suppliers.