I've got a list of designations for International Harvester Trucks, but for now, they're mostly after 1950. They're also primarily for light and medium-duty trucks(the letters, at least), except for the Metro Vans and Scouts:

LETTERS:
1)1950-52: L-Series.
2)1953-55: R-Series(remained part of a specific group of heavy-duty trucks until 1972).
3)1956-57: S-Series.
4)1957-58: A-Series.
5)1959-60: B-Series.
6)1961-65: C-Series.
7)1966: A-Series.
8)1967: B-Series.
9)1968: C-Series.
10)1969-75: D-Series.

NUMBERS:
1)1950-1962:
1a)110: 1/2 Ton
1b)112: 3/4 Ton:
1c)120: 3/4 Ton(Heavy Duty)
1d)130: 1 Ton.
1e)140: Milk Truck
1f)150: 1 1/2 Ton.

2)1963-1968:
2a)900: Light 1/2 Ton(1963-66)
2b)1000: 1/2 Ton.
2c)1100: 1/2 Ton(apparently heavier-duty).
2d)1200: 3/4 Ton.
2e)1300: 1 Ton.

3)1969-1970:
3a)1000: 1/2 Ton.
3b)1100: 1/2 Ton(apparently heavier-duty).
3c)1200: 3/4 Ton.
3d)1300: 1 Ton.

4)1971-1973:
4a)1010: 1/2 Ton.
4b)1110: 1/2 Ton(apparently heavier-duty).
4c)1210: 3/4 Ton.
4d)1310: 1 Ton.


5)1974-75:
5a)100: 1/2 Ton.
5b)200: 3/4 Ton.
5c)350: 1-Ton.
5d)500: 1 1/2 Ton.

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It's not much, but that's what I've got so far.