Is it worth the trouble or should I just use svn to do it.
I think it depends on how you much information you want to retain in SVN. If you do the merge using git, I believe SVN will not know where the changes came from, or in other words, it will look like the SVN trunk and branch is still separate.
Will people see I've used git and is there any meta data about the
merge in svn?
No, it would just look like a new commit onto trunk.
Can I do a clone of trunk and 1 branch I select?
If you mean clone your git-svn into a new git repo, then yes. Just clone the git-svn and delete the extraneous branches, or do that directly in the git-svn repo before you clone.
Here is a post how to convert an SVN repo to a git one. I think most of it would apply in this situation.
Do I need a full clone or can I import it from the point where the
branch was made?
Git clones will usually be full clones, unless you use the --depth
option. If you want to throw away the previous history, you can always squash all the commits into an older one, or just delete the .git
directory and init a new repo.