Masking a Ground Glass for Cinema Aspect Ratios

[r.e.]

I'm interested in masking my 4x5 and 8x10 backs (Arca Swiss F-line) for four aspect ratios that are used in feature films. I have two questions:

What’s the best way to mask the ground glass so that it’s easy to remove the mask and easy to clean up marks or residue?

Are there any issues with this approach to defining the image area that I should look out for?

This is not something that I've done before. Thanks for your advice.


Context:

Initially, I want to try this with the 4x5 back and the following Rodenstock lenses:

APO-Grandagon f/4.5 55mm
Grandagon N MC f/4.5 75mm
Grandagon MC f/6.8 90mm

I plan to try the following aspect ratios in landscape orientation:

2.39:1 (anamorphic widescreen)
Mask: 5” wide x 2" tall

2:1 (Vittorio Storaro and some Netflix films; also 12cm wide x 6cm tall still photos)
Mask: 5” wide x 2.5" tall

1.85:1 (standard widescreen)
Mask: 5” wide x 2.7" tall

1.78:1 aka 16:9 (high-definition television and on-line video)
Mask: 5" wide x 2.8" tall