OK.  The Gasket on the Wynn filter measures 17.5” OD x 12.5” ID, and it needs a flat surface to seal against. To accomplish this you will build yourself a Donut.

Then you can go Here to select the efficiency of your new filter.

How do you build a Donut? Basically it’s just a circle of plywood or MDF, with a 10” hole in the middle.  Some good examples of Donuts look like this:

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