I don't think it is too heavy for your boat.
I do think that you will find that taking the motor off the boat and putting it on may require some more people to accomplish. You should also take note of the water line before the old engine is removed and compare that to the line once the new engine is in place. You can reposition some weight (crew and supplies) such that you keep the boat balanced enough or reduce sail as needed.Is your old outboard a long shaft or 15"? The longer shaft engines are better for sailboats because of the rocking motion they can make with wave interaction. I helped a friend lift a fairly new 9.9 HP engine off of his H25 off his boat because the water pump seemed to be failing and the engine waw not discharging cooling water as it should. An astute measure as it turned out as if the engine would have been seized or have overheated on us had we gone out with the boat while counting on the engine. Just make sure all systems are working before you put the new engine under load (cooling, fuel, steering, leaking).