Giving reference to the parts manual, it calls out metal bushings. If you are going to floats or back and forth it's what is required. Also seaplane lip extension on lower cowling.
It's also a good time to inspect behind the firewall and give a look see at the ends of the engine mount stringers. I have found many that either have cracking in the stringer radius where the machined fitting rivets up (normally under the fitting @ outboard side radius) or intergranular corrosion gets going on that fitting. This is very difficult to spot so remove obstructions, clean the environment and use a strong light source and mirror to inspect. Bolt being removed helps a lot. Also elongated bolt holes caused by loose bolts. All three require replacement. No repairs are authorized.
Changing the bushings? yes support the engine and do one at a time but back off all 4 bolts to the last few threads you may need to unleash two depending. Engine mount may spring out of alignment when the bolt comes free but is easily muscled back into position with two or three gorillas and a ratchet strap or two.
Supporting the plane in two point, level, really helps. Oh, Pay attention to the bolt length requirements as well as any extra washers and type of nuts (parts book). You are ensuring that you don't thread lock and are able to torque properly with your recently calibrated torque wrench. 
