Help designing Calfo style box

[zojro]

I am in need of some advice before I drill. My tank is a 125 long (72"x18"x20") and I want to add a calfo style overflow that will span half the length of my tank. My plan is to drill and install 2 1" bulkheads to feed the skimmer portion of my sump. Water will be returned via a Quiet One 4000. What I am looking for is how to determine the dimensions for the box. Not the length of course but how tall and deep to make it. Also where is the best place to position the bulkhead i.e. high or low in the box. My main concern is noise. Any input would be appreciated.

Thanks