To make an LTM usable today, by which I mean it can integrate into other newer methods of attaching hoods and filters etc, then I would forget (regretfully) the early Elmars because you need to remove the filter to change aperture.

So choose a more modern lens such as a Summitar or Summicron, and get any necessary adapters (like Michael has shown above), and use modern filters and hoods. This opens up your choices and you don't need to scour the internet for rare or expensive items. All to often older lenses can throw up hurdles that turn them into niche purchases and not everyday users.