I have done that job on our D37. Just push the shaft out. Might have to use a wheel puller. If the seal is not a vented one then talk to the distributer and change it over to vented. They don’t sell non vented any longer. Also if your going to replace the bellows you should be replacing the carbon ring. Good luck.
Mine is a westerbeke with a v-drive. I assume yours is a v-drive. I can just get my hands under the pan behind the transmission. Not sure if that helps. I could send pictures if you want but not sure if that would help you. Also our boat is an aft cockpit with access to the enging by removing the stairs.
Well mine is a Perkins 4-108 with a V-drive so it should be very similar. Mine is a center cockpit, I’m not sure if that makes a big difference here. Pictures would be great, and smaller hands I guess!