Dan, If you want the set-up to feel exactly the same, then get the same lens. I've used different versions over the years. Personally i never liked the aperture tab on the V2, or the V4 versions with the
'tigerclaw' tab.....but that's my personal preference based on handling alone. As others have said, there is a choice of lenses out there and several of them are very good. Being in Tokyo, I'm sure you can check them out. The Nokton V2 1.4 lens that Ko.Fe. mentioned is very good, but not a close style match for the Summicron in image character. All the lenses you mention are old, and you'll pay a premium for one in pristine shape. If we're strictly talking Leitz lenses, to me, the desirable ones are the ones with the least plastic parts... but honestly those of us chatting on forums are the only ones who really nerd out about versions, the career photographers just used them as tools.