Hi Scott,
Couldn't find square. Also many replacement speakers require interior cut holes larger than the OEM Seaworthy. Wetsounds had the best that fit/sound quality I could find locally without needing to make the original cutout larger. For inside the cabin I used these...
https://wetsounds.com/pages/products/SW-65_spec.html
This is the speaker that I used for the four interior speakers. The cut out dimensions are the same, and the 2.6" depth isn't an issue on any of the tighter spots on the interior. The only thing you will need to do is drill new mounting holes (1/8th) as nobody makes a standard mounting 6.5" speaker mounting pattern. I just held the speaker in place, and drilled using the speaker as the template. Drill one hole, mount one screw, that will hold the speaker in place, then tackle the other three with a stable platform. They have a cardboard template in the box as well, but I found using the speaker works better so that the angle of the hole is 100% correct when drilling. I ended up having 1 of 4 of the old mounting holes just visible when I was done. I have a buddy with a 3D plastics printer who is going to make a quarter inch wide ring that will match the speaker cover in colour and go around the speaker to trim it and cover the one hole exposed.
For outside I used this pair....
https://wetsounds.com/pages/products/SW-650
https://wetsounds.com/pages/products/SW-650
They have a higher RMS rating, and are a 3.1" depth, otherwise they are identical in dimensions to the interior speakers. Mine are mounted just above the floor one the centre pedestal below the table forward of the steering wheel. At this distance they don't effect the compass but any closer they might as the magnets on these are very powerful.
It was a pricey but worthwhile upgrade if you enjoy music on board. They sound really good without amplification, but I'm considering upgrading to a new clarion stereo with one of their small 4D amplifiers (about the size of a deck of cards), to really make the system sing. I won't tackle this though until I'm done the rest of my refit items. It's been an expensive winter.
