Placing two additional guns on the forecastle at this late stage of the build (issue 108 of the magazine) was certainly a mistake. I simply forgot to do this earlier, when the access to this region would have been easier.
In the magazine, it is suggested that the guns need no additional rigging. But I think it was necessary to have them lashed to the deck so that they could not move about causing damage to the ship. Unfortunately, I have now idea how the guns were secured. So the following is pure fantasy: