The simplest way is what you just did: send them to the vim_dev list.
For new files, what you did is (I think) the right way to do it: as
plain text files including comments saying which one is for syntax and
which one is for indent.
If some day you propose changes to an existing files, a (context or
unified) diff is sufficient. For new files you could also have diff'ed
them to /dev/null but it would have made the atachments marginally
longer with no substantial advantage.
Best regards,
Tony.