I'm no expert, but my theory on purging/bleeding is that you don't have to run the cylinder all of the way in or out, you only need to make it stop moving so the pressure will build up. So, as long as a backhoe arm won't lift the tractor, you should be OK as long as it will attain full pressure by stalling.
As the cylinder pressurizes, the air gets pushed smaller and smaller into very tiny bubbles. After a few cycles, the bubbles all get displaced by oil and make their way back into the tank where they are free to effervesce out of the oil at normal atmospheric pressure.
Whether that theory is correct or not, the other posters are correct. Just run the cylinder a few times, and it magically starts working!
- Just Gary