Hi Sean
When you get the glass combo , and have tried it out could you post the results.
My suggestion is to try printing a negative that requires several filter combinations , therefore requiring you to do multiple exposures, .Try a print without glass and one with the glass. Pay paticular attention to the four corners of the print . Of course align the enlarger first for edge to edge sharpness.
have fun , I am interested in your results
Bob Carnie