The best way to accomplish that task is not with svnsync but with svnadmin dump, svndumpfilter, and svnadmin import.
Here are a few links with hints, examples, and code:
This way you will maintain all your revisions and also have a backup. This will also give you a chance to re-organize things, if you want too.
If you need any more help, i have moved a lot of repo's before, so feel free to post.