Starting with the L-series in 1950, the 1/2 ton models were designated as the 110, 3/4 ton as the 120, 1 ton as the 130, 1 1/4 ton as the 140, and 1 1/2 ton as the 150 (the GVW of the 150 reached into the 15,000# range, which bears little relationship to the "1 1/2 ton" designation sometimes used. The next heavier model was the 160, which evolved into the 1600 series Loadstar).
This numbering applied to the '50-52 L-line, the 53-54 R-line, the 55-56 S-line, then in 1957 the Golden Anniversary models restarted the lettering with the A-110 (thru A-150) models for 57-58, the B-110 models for 59-60, and the C-110 models for 61-62. '61 saw the addition of a C-100 as another 1/2 ton model with the torsion bar independent front suspension rather than the I-beam of the C-110 which continued to be available. The 110 was not a heavier version of the 100 as the numbering might suggest;the two front axles had the same weight capacity and everything else was the same. There were no 100 (or 1000) 4x4 models. The 140 series disappeared around 1960, with the 130 and 150 models covering the range.
A "major" change in the numbering scheme occurred with the 63-64 models when all model designations were multiplied by ten along with a restyling; the C-100 became the C-1000, with the other models becoming the C-1100, 1200, and 1500. In '65, the models became the D-1000 thru 1500. For '66, the letter designation was moved to the end and restarted at A; the D-1000 became the 1000A, followed by the 1000B in '67, the 1000C in '68, and the restyled 1000D in 69 and 70. In 1971, the letters were dropped and the models became the 1010, 1110, 1210, 1310, and 1510. No model number distinction was made between the 71, 72, and 73 models; they were all 1010's, etc., although I do recall the description 1010A being occasionally used in '71.
One odd-ball model was available from '63 through '67--a 900 model. Starting as the C-900, this was a stripped-down pickup with the 4-152 engine, 3 speed trans, and a 6 foot step-side box. By 1967, it had developed into the 908B with the V-266 engine and a 6'8" box in either a step-side or bonus-load style, but it was still a low-end, price-leader model. Another variation seen prior to '63 has the basic 110 or 120 model designation upgraded to 111 or 112 for optional GVW ranges of the model. The logo on the truck was not changed, but the paperwork would label it accordingly.
In 1974, the vehicles were again redesigned with coil-spring independent front suspension for the 1/2 and 3/4 ton 4x2 models, now designated the 100 and 200 series. The 1510 became the 500 series, but did not get IFS. There was no 1 ton 300 series, but the 200 series had the optional axles and springs from the 1310 to cover the weight range.
In 1975, the 100 series became the 150 series with a minimum GVW of 6200 pounds so that it was not necessary to meet stricter light-duty emissions laws which applied to vehicles with GVW's of less than 6200 pounds (the same reason the Scout was designated Scout XLC--Xtra Load Capacity with a 6200 GVW in 1975). Other than suspensions, no major changes were made in the trucks.
Travelalls were available in both of the 1/2 ton models and the 3/4 ton model and carried the same numeric designation as the equivalent pickup. There were no particular differences between the models other than the chassis capacity. I do not believe there was ever a 1 ton model Travelall, although I have learned to never say never with regard to variations that may have been produced. Fred Crismon, author of the Crestline "International Trucks" book, refers to a 1300 series for one of the 10-door Airporter conversions of the Travelall and SE options may have produced the equivalent of a 1300, but it was not an advertised model if it was actually a 1300. The first use of the name Travelall appeared late in '52 although earlier conversions of panel trucks to wagons had been done. The first Travelalls had only 2 side doors, a third door on the passenger side appeared with the A-line in '57 and the fourth door arrived with the C-100 model in '61(sounds like club cab pickups in the '90's!)
As you can see, there was some rhyme and reason to the numbering scheme that evolved over the 25 years it was used. Actually, the scheme began with the K-1, 2, and 3 designations that began in 1940 and can be traced back to numbering schemes used in the 1930's, but the designations did not always follow the pattern during this period.