Sometimes these old things can be so frustrating to get off. 20+ years of rust, neglect, and abuse and they might as well be welded onto the shaft.
I unsuccessfully tried other methods including soaking with various chemicals, prying with piece of pipe, hitting it with a big hammer, wedge blocks, then some plates I made to press it off using bolts, tried heating with weed burner.... Those stump jumpers were just stuck forever.
Time for drastic measures. Time for hydraulic press.
Made a weld on press bracket with 3" channel and rectangular tubing. Welded it onto the stump jumper and added bottle jack. First one came off with ease. Second one was still really stubborn. The welds of the bracket to the stump jumper broker free. Then welded them back on adding welding along the 3" web, then jacked till really tight then heat. Finally.
This was necessary on this bush hog because the access holes to get to the nuts were not aligned up. They were under the main support channel and rusted in place. It took much heat with the torch till the nuts were red hot to then get them off with impact. Then it took the 16# sledge to get the bolts out of the stump jumper to get the blades off.