I received the Technic bars today. Unfortunately they are "dark" grey instead of black. So first I measured where I need wholes in the covers of the alt mode to attach the cannons and then drilled them in. Then I cut the bar into pieces to be connectors for the Technic pins. They will be fixed in place with hot glue and/or Apoxy sculpt. And I drilled wholes into the cannons to put the pins in. They will be fixed in place by hot glue, too. I haven't split the cannons yet. I will do this at the end because I think it's easier to make everything fit together while the cannons are not seperated.