Though the driver hole or one panel held on temporarily, for example. pipe not glued and located so that you can reach it. Just plan it beforehand so you are able to do so if necessary 😉 My reflex plumbing pipes have been too long many times.I am guessing that this would involve being able to take the face off to adjust as the ports will be inside the box itself..
Re: Port Centre Line, the attached image should show you what you want to be doing I hope.
Not quite. 🙁 The bend is a bit more complex: The Subwoofer DIY Page - Horn Folding
GM