Seeing that you are dealing with a '54, most likely the bushings are pretty well shot. I replaced the ones on my '50 a couple of years ago, and I don't remember having to remove the bracket attached to the cab floor. I had some wooden wedges that I placed between the frame and the cab floor and then removed the shackle assembly. Once that was done, I drove out what was left of the bushings, put the new bushings in and replaced the shackle assembly. ( A little PB Blaster to persuade the nuts to come loose, and a little silicone spray on the bushings to persuade them to go in the brackets will make life a whole lot easier). Once the assembly was back together, I knocked the wedges out--Job done.
