I'm starting to convert my ESL-63s into ESL-989s by mounting the drivers in a 3060 t-slot frame. There will be separate 2020 frames to hold the dust covers and a 1/2" wire mesh on the back and front sides of each speaker. Those two frames will be held on the main 3060 frame with 3D printed brackets that will mount on the 3060 frame with screws and t-nuts, and there will be additional clamps the hold the 2020 frames securely against weather stripping tape on the 3060 frames.
Here's one of the 3060 frames set up in front of the ESL-63 on its stand:
Here it is with one of the blue 2020 dust cover frames in position:
Here's one of the corner clamps- they screw directly into the ends on the horizontal members of the 2020 frames:
Here's a CAD render of the dust cover clamps.
The clamps are elliptical and stand out beyond the frames so they will support cloth socks held away from the underlying speaker frames/mesh. I intend to use thin, stretchy material for the cloth socks, hoping that the resulting speaker will look somewhat sculptural. In the end I may not use socks on them at all, in which case the clamps will be redesigned/printed.
When it's done I intend to be able to remove the mesh/dust covers by unscrewing the middle clamps from the 3060 frame, and unscrewing the 4 corner screws from the corner clamps. I expect to be able to replace the dust cover frames without having to install new film.
I'm also looking at using Wago 221 lever nuts to wire the drivers so that there will be no need to solder and unsolder wires in case the speaker needs to be serviced.