Zero P-51s were shipped with a Malcolm Hood. All that received a 'hood (B and C) were modified in the theatre service centers and maybe a few by individual Firgther Group Service group at the base level.
When introduced into the 354th, 357th, 355th and 4th the mods went to senior leaders that wanted them - first - and went first on the P-51B-1 and -5 before the first C's.