You can do it with the engine in place. You do need to disconnect the water hoses. You can loosen all the bolts but unbolt one side at a time (keeps the block lined up for re mounting). Place a large block of wood under the oil pan and jack up just a LITTLE (too much and the carbs get in the way). It helped to loosen the gear box mounts to get a little more clearence. May as well replace them while you are under there. I did this a few years ago so I hope I am remembering every thing. Jack stands, wheel chocks, safety goggles, band-aids and Guinnes.