I finally got the beast up and going...
I happened to have a WD 160GB drive laying around so I threw it in. It formated and loaded the OS no problem. The result: 128GB after format. I was figuring about 110-112GB useable after formatting a 120GB drive, so I did get my extra 17GB I was looking for, however I didn't get the full 137. Perhaps there is a formatting trick that will allow me to do this as re3dyb0y suggested, however I doubt it because if the snap only sees the first 137GB, it can't format any more than that, so the result is always going to be 128-130GB usable. Again though, I got my extra 17GB and the WD 160's are only $3 more a drive than the 120's.
Just wanted to give an update. I am one VERY happy camper right now