Hi Chris, welcome on board.
I suggest you go here, and read Arne's Junk Rig for Beginners, for a start. This will tell you a lot about the mast placement, why they appear to be so far forward, etc and more about junk rig generally.
After that, why not put Vivacity into our Search Engine on the Members' Area page? Then you will come across two members, Dag and Mark, each of whom has a Vivacity. Dag has the yawl that you have seen. You could contact these people about their experiences, if you wished to.
After you've done this, you will have a bit more idea of what it is you are trying to do and can then ask more particular questions about details or your individual project.
As I recall, the Vivacity has a good name as a small cruising boat. Best of luck, if you decided to go ahead.