Here is a listing of the zone office locations as of 1969, from GM documentation:
1 Flint MI
2 Tarrytown NY
3 St. Louis MO
4 Minneapolis MN
5 Kansas City MO
6 Oakland CA
7 Dallas TX
8 Atlanta GA
9 Cincinnati OH
10 Denver CO
11 Chicago IL
12 Buffalo NY
13 Pittsburgh PA
14 Baltimore MD
15 Philadelphia PA
16 Charlotte NC
17 Memphis TN
18 Des Moines IA
19 Portland, OR
20 Los Angeles CA
21 export
22 Louisville KY
23 Oklahoma City OK
24 New Orleans LA
25 Indianapolis IN
26 Jacksonville FL
27 New York NY
28 Cleveland OH
29 Omaha NE
30 Houston TX
31 Birmingham AL
32 Boston MA
33 Fargo ND
34 San Diego CA
35 Newark NJ
36 Salt Lake UT
37 Richmond VA
39 El Paso TX
40 Charleston WV
41 Wichita KS
42 Seattle WA
43 Portland, ME
44 Detroit MI
45 South Bend IN
46 Green Bay WI
47 Peoria IL
48 Syracuse NY
49 Harrisburg PA
61 Milwaukee WI
These are from various Canadian sources - not a definitive as the above list, but I believe they are correct.
80 Oshawa ON
81 Vancouver BC
82 Calgary Alberta
83 Regina SK
84 Winnipeg MB
85 London ON
86 Montreal Quebec
87 Moncton NB
88 Ste. Foy QC
95 Toronto ON
96 Ottawa ON