If you’re installing a ‘drop down’ screen, couldn’t it be dropped down to different degrees to accommodate different ratios anyway?
Or if you’re really serious about doing this right, have a fixed 2.40:1 screen and put in a motorised curtain track to add/subtract masking like real theatres used to do.
I’m looking at a Seymour screen and they said it can only be programmed at the factory to drop down to a fixed point. It can’t be adjusted at will, unfortunately, but thanks for the thought.
There are, as you suggested, motorized systems from Stewart, Screen Innovations and maybe others, but they are VERY expensive. Seymour does have a masking system which is less expensive. Thanks for your help!