Perfect! I did that, and I've already heard the siren zombie (in the distance, thankfully) on my test map, so it appears to be working, BUT I am also randomly (I think?) hearing this sort of DING! sound occasionally. Could that also be related to the siren zombie?
I think the line numbers have changed. Would it now be 319 and 640?
Additionally, if I only wanted to use on special zombie to start (and add more in later), I'd just comment out all the others from the eight groupings at the top?