Look at the pics in the link:http://home.comcast.net/~old_allis/ac-wd45d-clutch.html
If the bronze part that you are talking about is actually the shifter collar, held together by two bolts, then acwd45man may have good advice. After removing the side rail, it is the shifter shaft that you have to remove in order to drop the shifter fork to provide access to the bolts on the shifter collar. I believe that the access to the bolts is tight, but maybe doable as I think I found a cobbled wrench that my Dad used to do this fix years ago.
If the shifter & bushings are damaged, you have to split the tractor between the transmission housing and torque housing and back the splined drive shaft for the transmsission out of the engine clutch shaft, while sliding the transmission clutch pack off the shaft.
If complete splitting of the tractor is daunting, you can use 3/4" threaded rod to replace the bolts in the siderails. Support the front of the tractor with blocks and back the rear of the tractor away with a floor jack enough to remove the wet clutch & shifter. That is, you stretch the tractor rather than entirely splitting it.