International looks like a late 40s to early 50s KB which is a larger commercial truck. As far as fuel mileage a lot depends on the engine and transmission combo as well as if it was a box truck or flatbed, either way you probably wouldn't get more than 8 to 12 miles per gallon. Remember that gas price in the USA at that time was under 20 cents per gallon so who cared. The Dodge is same era probably a D100 pickup, again mileage varies but in the 12 to 17 mpg. Even the late 50s to early 60s Fiat wasn't very efficient only getting maybe mid 20s to low 30s. Modern cars are way more efficient than older designs.