the D-7 fire was a Special Effects mistake or error in judgment. Nothing is supposed to fire weapons from the nacelles to my knowledge. I think they once had a phaser beam or torpedo come from the main deflector of the Enterprise D too at one point. Something along those lines To my knowledge, the only weapons that the K'tingas have are forward and aft torpedo tubes.
Is that a canon source? I highly doubt it is. The following, however, is from Star Trek: The Magazine, which doesn't print any non-canon material. It has the positions of all weapons emplacements: [link]
I don't know if it's canon. You see, I have my personal canon on TOS so it would not interfere with the crap of the TNG era. For me, Franz Joseph, Mr Scott's Guide to the Enterprise and the FASA manuals are strictly canon