Hi Swift, I was one of the Brit contingent of six bikes that went over this year (Indian Scout #563AVG) & intend going back along with Briz & a few more in 2014. This was our first trip & we learned an awful lot, not just about our bikes but about shipping, dealing with the US authorities regarding paperwork, & transportation/costs/living etc once we got there.
The first thing you should do is get a copy of the rule book.
There's a full account of our time in the USA on the Brit Chopper forum, in the form of a section called "The Bonneville Blog"
http://www.britchopper.co.uk/forum/ You'll have to register to read it, but well worth a look. We were also followed by a BBC documentary film crew (2 x 1 hour-long programmes, BBC2, January prime-time).
Riding at Bonneville is the BEST thing I've ever done, & I've done a lot! You can get me on 01493 733695 if you want to chat, but you might catch "Salt Fever".