That weight on the J series is incorrect, the shipping weight on the J series is shown as 6850 lbs, and for the early U series the ship weight is 6870 lbs, the later U model is 7430 lbs.
I have changed the figures to the ones Josh has given. I imagine there would be differences between 3j and 5j tractors as well. Josh, are the figures you gave for 3j or 5j ?