For anyone still having trouble winning in the F-100, the following makes it easy:
Upgrade the F-100 with the AWD conversion, max all the engine upgrades, max the tire width front and back, and add the 2-way diff.
Select a Cross Country Race in Blizzard Mountain. I choose "Lower Slopes Cross Country" because it goes over ice multiple times and the F-100 can get the kangaroo skills easily. Create a blueprint and choose "1960s" as the car class. Then set the weather to "Blizzard".
The F-100 will be the only competing car on snow tires and you will be the only AWD F-100. The AI will be extremely slow over the icy sections of the course. It should be an easy win.