firstboot postflight

I have a slew of preferences settings for my build, and I read that these settings should go into the firstboot postflight script. I found the firsboot script in the firsboot.pkg - I added the firstboot postflight.sh in the same folder as the firsboot.sh file. My question is: is that the correct name for the postflight script? Also, is there anything I need to do to make sure this script will get executed during the instaDMG build?