I have replaced them one at a time. You need to remove all the nuts leaving the bolts in place then jack up one corner. Pull out the old and install the new then go around that way. There is enough flex in the mounts to make this happen. A couple 4x4's nailed together will spread the load out. Leave the bolts in and replace them as you go keeping the nuts off until your finished. This will keep the cab located and avoid it "shifting" as your jacking up a corner.
I have also just dropped the column, shifter linkage, etc. Then lifted the cab up 4-5" with a engine hoist and straps under the body to slide in new bushings that way.
Your fenders and front clip do need to come off of course. Going to need to do it anyway to change out the front clip bushings. I have done this without removing the bed before. But that was because I was being lazy. You can pick the bed up with a cherry picker and slide it 6" back setting the thing back down on wood atop the frame to avoid potential scratches to the cab.
Generally your electrical will have enough play in it to lift the cab up 4" without pulling on things. But keep an eye on things while lifting so you don't rip any thing like a ground strap off.