A. So you're considering a Virago Trike? Try this page, right HERE. This isn't about Virago trikes, but it's an excellent guide to designing one from scratch. It is written by a man by the name of John Partridge in Plymouth, England.
Comments: As I am also trying to get information on trike design for a future build (from a different model Yamaha, not an XV), this site is a Godsend. It's a bit long, really, but once you start reading it you'll see he's covered everything you need to know to start building your own. And he's got a wicked sense of humor.
Additional Information; You may also want to check out this page for wiring help on your trike.