In most cases a rattling damper plate, where the rattle stops with a slight increase in rpm, is not an emergency repair situation. You might consider doing the repair as part of your next haul out and have the props and shafts checked at the same time. Depending on how your engines are mounted determines some of the level of pita. It’s less if the rear engine mounts aren’t connected to or with the bell housing, more if it is.
I have a legacy product similar to the suredrive coupler
https://www.suredrivemarine.com/ They are attached between Hino EH700 engines and ZF Hurth When the rubber bumpers wear to the point of a significant idle rattle,