The older piston is fairly well scored, Mark. Personally, if I had a spare piston I'd use it, because the rest of the engine looks decent.
My system for getting by without a timing mark on the crankshaft timing gear, is I put the crankshaft on TDC, then insert the camshaft so that its timing mark is at the closest point of approach to the crankshaft. Of course you have to allow for the spiral gears, so you enter the teeth nearly 1 tooth anti-clockwise from where you want it to end up. I prefer to use a pair of timing marks, and that is why I make one before taking the camshaft out, but it isn't actually necessary, and isn't recommended by Honda. In case you care, the reason there is no mark on the steel crankshaft gear, is that it isn't keyed to the crankshaft, it is just pressed on. Honda recommends pulling it off and replacing it if if gets worn or damaged, so they couldn't have put a timing mark on it in the factory in case the owner later removed the gear and replaced it, in no particular position.
