Mine is 10"x7.5". I read somewhere that 75" is a good number for the port. My cabs also had the horns stuffed in the bottom when I got them. I had to cut a piece of plywood for the port area because that piece was missing.
The current port sounds much better than A7's I have heard with factory ports. Mine are tuned much lower. I would try other sizes and experiment but I like this setup too much

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