Found this. - don't not how accurate it is.
DSO codes are 6-digit numbers.
The first two numbers are the District code. 62 Houston (65/71)
The remaining four numbers are the actual order number.
D.S.O 1965-1973
District Code
11 Boston
12 Buffalo (65/66)
12 Buffalo (72/73)
13 NewYork
14 Pittsburgh (65/66)
14 Pittsburgh (72/73)
15 Newark
16 Philadelphia (67/73)
17 Washington (67173)
21 Atlanta 54 Omaha
22 Charlotle 55 St Louis
23 Philidalphia (65/66)
23 Memphis (72/73)
24 Jacksonville
25 Richmond
26 Washington (65/66)
26 New Orleans (72/73)
27 Cincinnati (67/68)
28 Louisville (67/3)
31 Cincinnati (65/66)
32 Cleveland (65/71)
33 Detroit (65/71)
34 Indianapolis (65/68)
35 Lansing (65/71)
36 Louisville (65/66)
37 Buffalo (67/71)
38 Pittsburgh (67/71)
41 Chicago
42 Fargo (65/68)
42 Cleveland (72/73)
43 Rocktord (65/66)
43 Milwaukee (67/73)
44 Twin Cities (65/70)
45 Davenport (65/68)
45 Lansing (72/73)
46 Indanapolis (69/73)
47 Cincinnati (69/73)
48 Detroit (72/73)
51 Denver (65/71)
52 Des Moines (65/68)
52 Dallas (72/73)
53 Kansas City
56 Davenport (69/73)
57 Houston (72/73)
58 Twin Cities (72/73)
61 Dallas (65/71)
62 Houston (65/71)
63 Memphis (65/71)
64 New Orleans (65/71)
65 Oklahoma City (65/71)
71 Los Angeles
72 San Jose
73 Salt Lake City
74 Seattle
75 Phoenix (67/73)
76 Denver (72/73)
81 Ford of Canada (65/68)
83 Govemment
84 Home Office Reserve
85 American Red Cross.
87 Body Company (71/73)
89 Transportation Serv.
8D Shelby Unit (68)
90-99 Export