Correct. Since your old save was made in a game version before 1.0.252, it isn't in the new compressed format, so it is only the new save you need to worry about unpacking.
Well, I finally got around to actually transferring my current game to the latest D:OS and Source Difficulty versions, and it appears to have worked like a charm.
So, all I needed was to copy in the new meta.lsb file, yes? All of the other files could remain intact? (Everything appears to be working just fine, but I want to confirm.) I did move the .lsv file as you mentioned, Raze.
Thanks!