Just mark the chain and cam sprocket with some paint for a getting back together party. Make sure the cam position on the replacement head is at the same place as the old one on the engine before putting the replacement head back on is more important. Cam marks line up on the original head before pulling it and simular position on the complete original head before it is installed.

You cannot rotate the cam into position on a fully loaded installed head after it is bolted down without disabiling the valve train first. The chain will remain timed on the crank sprocket that has a tang underneath it so the chain cannot drop off and the injection pump sprocket timing tends to not be effected either.

Getting it all clear in your head before doing it is the best.That way it is not hard and you get no suprises. You may already be well aware of this but just in case. It is not hard at all if you think it through.