I have two Model M keyboards, the main one (using it right now) and a spare one; needless to say that the spare one is still unused since the main one doesn't want to break after 28 years! Another possible mod for the keyboard, although purists would possibly not like it, is upgrading the controller board so that it speaks directly USB. Here are some pages I found on the subject:

https://github.com/mschwingen/hardware/tree/master/modelm-us...

https://blog.lmorchard.com/2016/02/21/modelm-controller/

https://www.crackedthecode.co/how-to-supercharge-your-ibm-mo...