Those bushings have a step(larger OD), in them, towards the main frame bracket.

When I did mine, I removed the "wheel module"; then knock out bushings, but had to be extra cautious when installing and "lining-up" those new bushings, just as they started to go into the "wheel module frame".

 For the stubborn ones; I had to use a couple pieces of flat plate steel, with a center hole, and used some threaded rod to add just a little tension to try and squeeze the bushing inward, but then eye-balled it and use some taps, with a hammer, to make sure it was "square", before I tightened the threaded rod some more, then tapped again with hammer. Just keep "eye-balling" them , to insure they get started straight and square.

Also, during reassembly onto planter, I notice quite a bit of clearance, between wheel module and main planter frame bracket = I decided to add a 3/8" hardened washer on that round tube to spread the planter frames apart a little more, but still have free movement of travel, for the wheel module frame to go up and down (pivot). This achieved a little more bushing material to support the load, also. 

(tool to pull in bushings.jpg)

(wheel module frame bushing 3.jpg)

tool to pull in bushings.jpg (29KB - 64 downloads)

wheel module frame bushing 3.jpg (94KB - 55 downloads)