From memory there are lines scribed in the side of the cam sprocket that are to line up with the top of the head, this should be at TDC on one piston (type I anyway).
The cam is in halves. The end covers (or something under them) hold the outer cam bearings in, ie the points cover on one end and a plain cover on the other end. The cam halves pull out the sides through the bearing OD holes.
The cam halves connect with a spline missing one tooth so they don't go together "wrong".
I would just find the chain master link, remove it and tie a string to each end, then lift the head off without turning the crank. I expect you'd hit a valve if turned but no reason to turn it if you want the head off. To just change a chain in place you link on the new one and pull it through while held to the sprocket. With the tappets out all the way it turns fairly easily.
With ball bearings I suppose the cam has to be in halves. Hiding the spark advancer in the middle is a bit of a trick! Make sure the points shaft is a snug fit in the cam; the ignition timing goes all unstable once it gets loose and starts wiggling around. I think there may be bronze bushings in the cam? Anyway I have a cam and advancer set that's worn this way and haven't had to try and fix it.
