To tell the truth, I've been very reluctant to take mine off. My tractor sat outside for two or three years (that I know of) before I got it. I have no idea if it ever saw the inside of a shed with the previous owner.
It is also missing the guard over the PTO pulley, so I just use it for lawn mowing and to move the occassional trailer. I do have my Dad's AC WD for real tractor type jobs, though.
I just went out and looked at mine, you did take the three bolts out that hold the splined hub and sheave together, right? On mine, there is enough room to put a hefty prybar between the two, so maybe you could work it one side then the other?
If you have time to wait, try leaing tension on a gear puller while soaking with your favorite penetrating oil.
Robert