Yes the offset keys are available, but; remember, the four degrees you are seeing is not a scientific, dial indicator type measurement, it could be more, or it could be less. Additionally, in my way of thinking the worst thing about a stretched chain is not the fact that the cam and pump timing are off, but rather the risk of chain breakage. As these pins and bushings wear, the risk of timing chain breakage increases. On the other hand, this is a double row chain which is quite strong. A broken chain would probably be the result of a broken guide or some other event jamming the chain.
Changing the chain is a personal decision. Although it PROBABLY will not break, the ease of changing it should be weighed against the catastrophic effects of a broken chain.
Best of luck,