Well, after yesterday's failure I at least got some reassuring news today.
I was able to get the precision port to fit on the pvc after some grinding.
From the front it looks pretty much flawless. From the back, (which I don't have a picture of) you can see the precision port's ID is a hair smaller than the pvc's ID. I'm not sure if I'd try grinding the inside of the pipe though as that's a bit more tricky
How much would the magnet move? I can easily give it a big enough opening so that shouldn't be a problem.
I'll need to look into the port clearance issue. I think it should be ok if I put the elbow closer to the back of the box and I can even shorten the port a bit so I should be able to get the necessary clearance.
So, I spent some time learning sketchup today and I think I got it 99% done. The only thing I might need to do is make the front piece 25x25. Currently it's 25"x23.5" tall, so the outside of the front port flares overlap with the top and bottom a bit. I'll need to see if it causes any issues with the cut list.
In the third picture the distance between the front of the interior port and the back of the front brace is 4.25 inches
I also totally guessed on the dimension of the speaker magnet, so that will probably need to be adjusted.
I was trying to find some way to put in some more bracing perpendicular to what is there but couldn't find a great way to add it