I have a West Marine 310 inflatable. I carried in on the platform of my prior 320da. No davits, we just strapped it underneath to the cleats. It fit fine. It would fit well on a 340. Somewhere around here I have an unused dinghy sling (google it). I love the thing but never used it (!). Nice way to carry a dinghy without davits. I never used it because I went to a 400db that had a davit system.
i did a 310 on our 290 lol. It was something to see and it liked to fill up nicely with water coming down off plane. If we would go on long trips I would just deflate it and stick it under the rear bench