Blueflame don't do custom as far as I know, at least not normally. Mine was definitely "off the shelf" anyway. You can choose from two different tailpipe options but that's it, and that part bolts on anyway so it's just a matter of them chucking a different tailpipe into the box.
One thing to note with the Blueflame 350Z system is that they have recently removed the silencer from the mid pipe to make it a little louder as some people thought it was too quiet. The problem with this change is that it means all of the sound clips on the website are even less representative!
Mine is one of the older ones with the mid box in place and I can see what they mean as it really isn't much louder than stock once you get over 3000rpm, although it is a bit more deeper sounding lower down in the rev range. Rather than get the new mid pipe I've decided to chuck some HFCs on and see how that sounds.
Fit and finish are excellent by the way!
Someone on here recently bought the new spec Blueflame but I don't think they've posted their thoughts on it yet. Might be worth dropping a post in this thread to see if you can get any more info:
viewtopic.php?f=62&t=31452
From the Blueflame site...
http://www.blueflameperformance.com/custom.php
Also a quick search on here for "blueflame" will throw up at least one of the earlier custom jobs.