I guess I just figured that if you put two double barrel tubes in the front, and two in the rear, it makes eight.
But you are right, maybe four is good. And as for story fodder (what with Captain Clark and the Miranda-class Ulysses) I did a short video about that with crappy special effects about a year ago. Did it in only two days, too! Here's the link: http://www.youtube.com/watch?v=yZeRy0IfpXE
UPDATE: I have discovered that there was a Nebula-class USS Ulysses around the same time that I had planned to launch this ship (DS9 Episode "The Adversary"). So this whole project is now in jeopardy.