it would probably come close if you put in all the numbers right. Horn Resp does not take into account losses from panel vibration so it would probably lose a dB or two there, but the driver would probably shred rather quickly.
That is just the area of the throat at specific points in the horn path. If you just use the measurements on the plan, you should not go wrong, unless you are trying to modify the design, and then you will have a fair bit of math to do. I would say just stick to the plan.
I think MDF is denser and sounds better, but there are concerns about joints cracking under the weight of larger MDF boxes. Also, MDF is extremely moisture sensitive. If you built them for an install MDF would be fine. If you are carrying them around, I would recommend birch.