Waz,
Email me the size and how many holes you have in the top layer (board below riffle box) and I'll cut out some rubber insert flaps for you to stop the fines dropping into the bellows below.
Looks like you still have some work to do to find the real bellows type dry blower cloth. (Had my doubts with the Reeds cloth which is for Keene's constant air which is designed to have fines/gold drop through the cloth???)
I realise it would be a pain, but maybe you should silastic the holes in the original cloth and refit, then you would see how your Wizard should work. (Minimal to no dust/fines dropping through the cloth.)
Cheers
Peter