First attemped, still single direction, I wrote a evolution to gtodo converter.
I’ve took a quick peek at the source of multisync and that realy helped me to understand how it works.
The trick now will be to make it sync both ways. This should be relatively easy, because I have last-edit date availible on both side, and I use the creation date (that evolution also use for his id), as id in gtodo.

Offcourse there is a screenshot: http://images.qballcow.nl/gtodo2-evolution.png?orig=1