Solid tire headaches

I have a Bobcat 21" mower with ten inch rear wheels upon which are mounted solid tires. These are drive wheels in that each rim has a pulley bolted on which receives a small drive belt.

I want to change out the bearings, but it is clear to me that each bearing is sealed within the two-piece steel rim, which is bolted together with the same three bolts that affix the drive pulley. Initially I expected to press out the old bearings and press in the new, but the bearings are significantly larger than the opening in the rim, which allows only for a bushing over a large axle/bolt. Plus, the bearings match these wheels by part number, so I believe I have the correct bearing. It appears the the unit was assembled over the bearing and the rubber tire.

There's no rust, but these rims are pretty well wedded together. Any ideas for loosening them without destroying the whole thing?

Thanks!