I've given in to temptation and an now the owner of a contemptor dreadnought from Forge World. One of the weapons that I've selected is the Kheres. Today, I wanted to show what the bits looked like right out of the box (pictured below).
What is clear from these bits is that getting the orientation of the rods for the cannon in the correct sense is important. They are not symmetric: they must be inserted in the main body of the cannon so that the fit. At the other end, they are symmetric and will slot in to the terminus of the cannon nicely, but even so it looks fiddly to say the least.