I had similar issues on the Yanmar 3JH3E on my 2001 H380. The pump's lower starboard bolt backs out into the engine mount, necessitating removal of the mount.
After removing the engine cover/ladder (pull the gas-strut first), I supported the engine with a ratcheting strap off the boom. No need to actually lift the engine, just support it. In fact, I probably didn't need to support the engine, given the engine is still supported by the other 3 mounts. I pulled the alternator, just for access, but probably don't have to. I barely loosened the big (15/16") upper-engine mount nut, then removed the lag bolts (14mm) holding the lower mount to the hull. This allowed me to rotate the lower part of the mount enough to access the 14mm bolts attaching the upper engine mount arm to the engine. Once the engine mount is off it was all lickety-split easy. The pump comes off with 12mm socket; expect a tablespoon of engine oil to dribble out. Prep the gasket surface, new pump on, hoses on, seacock open, alternator on, go sail.
Remember before all this, to close your seawater intake, label your alternator wires, and have a rag handy. Don't adjust the lower nut on the mount that the engine actually rests on; it is set to align the engine with the transmission/prop shaft.
