First FON (factory order number) of J45s in 1942 was 907 (and 923).
Bracing for FON 7xxx H and some 9xx FONs was basically the same as the third J-35 issue of two nonscalloped tonebars.
After WW2 the J-45 stayed sunburst, with a blond version being introduced in 1947 and called the J-50.
But in reality the J-50 preceded the the J-45 by one month.
This style of J-45 with the striped pickguard and circle logo tuners ended around FON 2221.
tall and thin back braces, 24.75" scale, 19 frets total on fingerboard.
dot fingerboard inlays, "Only a Gibson is Good Enough" gold banner logo, brown sunburst finish.
Note 1942 models have higher tuner position on the peghead, leaving less room for the banner logo.
This was changed in 1943, moving the tuner slightly closer to the nut, giving more room for the banner logo.
(Easy to see, 1942 models have the "D" tuner almost touching the bottom of the "G" in the Gibson logo.) Note there was a batch of a few natural finished J-45N (or J-50 if you prefer) models made during June 1942 (see pictures below).