So the brown sets did have matching cords and dials after all! Shouldn't this phone have a straight handset cord?
Both types were available when this phone was manufactured (9/55).
H4BG (straight) --3 (black), --50 (ivory), --52 (gray), --54 (brown)
H4BH (retractile) Color codes --50, --52, and --54
TCI Library: (C36.101 issue 13, May, 1955) Table on Page 2: Handset Cords
Also, C32.535 was revised (Issue 5) in May, 1955 to include color 500s:
2.11 Cords: Neoprene or vinyl-jacketed handset and mount-
ing cords are used with 500- and 501 type sets. The
handset cords contain four conductors. The mounting cords
have three conductors, except those for the 500H and 500P (six
conductors) and those for the 500L/M (four conductors.) All
3- and 4-conductor cords are available in the retractile type,
which is only installed when authorized by a service order or
other local instruction.