So back to the drawing board and back to McMaster Carr.
So I'm going to try the highest flow perforated metal I can get, 79% effective ("open") area compared to the stock S&H 28% effective area.
Use that perforated metal for the sides and top of the filter.
And I'll use a 30 PPI (Pores Per Inch) "course" 1 inch foam for the filter material and I may
oil it although here on the Central Coast dust is not an issue.
This foam will flow substantially better than the stock S&H green foam which is probably 60 to 75 PPI fine foam.
We'll see how it turns out next week.
Cheers
Greg