Looks like the water was in there a while. Water in the carburetor is of no great importance, but a valve stem rusting onto the guide means water inside the engine. Let's hope the crankshaft journals are OK. As a first guess, the water got in there after the mower was tossed out by a contractor due to oil smoke. Hence there was probably an oil film at least on the big end journal and the bottom journal. The top main bearing is a ball race on GXV Hondas, let's hope the water didn't get up that high. I think the odds are pretty good.
I suggest you remove the flywheel, open the crankcase, lift out the camshaft*, dismantle the big-end, pull out the crankshaft, and pull out the piston and rod. Remove the piston rings, measure the cylinder bore diameter, and then measure the ring gaps. Take out the tappets to check for rust. Check the camshaft for rust.
*GXV Hondas usually don't have a timing mark on the crankshaft timing gear. You can get by without one, but I always make one with an automatic center punch before I pull out the camshaft.
