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The standard table insert needs widening (to approx 1 1/4 by 10 1/2) where as the dado needs extending and a slot cut for the riving knife / upper saw guard and grinding out the center tabs so the ZCI can be rectangular without other mods.
The bottom
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just needs a couple small brass bars epoxied near the ends, but extending far enough so the ZCI has enough support to not fall through.
The bottom lips of the table and dado insert are 1/2" deep so there should need to be any shims etc. to make 1/2" stock work.
Just cut the MDF, ply or whatever to size (1.25 by 10.5 or what ever you make the opening) drop it in, use what ever means you fell most comfortable making the blade opening and you should be ready to rock and roll.
If you feel you need to secure the ZCI, then you could drill a small hole (or holes) through the brass bar (s) which could be used for securing a small brass screw to the bottom of the ZCI.
Be well,
Ben
Thanks to Dusty for the table insert drawing!!