You don't have to break the cam chain to do anything to the engine, the cam chain shouldn't have to be replaced (unless maybe it sat for decades with an engine full of rain), and it's trivially easy to time the cam no special marks required. To do it, line up the timing marks on the crank and put the camshaft back in with the mark on the sprocket as vertical as it will get, with the chain tight in front. Very simple. An overlooked thing to be careful of is the camshaft should be centered left to right properly and then the bearings should all be as inward as possible so there's no play. When you put the top cap back on, make sure all the adjusters are very loose.