From my experiences (some time ago) the hassle of exporting is all at the receiver's end of things. I imagine that exporting to Britain would still be very easy as this is a British made bike, but that the new owner would have a lively time with the new documentation paperwork and so on. That wouldn't be your problem, though. It's not hard to crate things up and get them sent out - although crating can be a chore. I'm not sure if it's easier to send a bike that's dismantled/incomplete as spare parts or as a whole bike, these days. I never had much trouble either way.
If you'd like to sell within the US why not send interested people from this site some pictures? Some of us live in the US! I might be interested.
Shipping to the Uk is not too expensive. Shipping ports of San Francisco or Houston. Cost in a container to the UK is about £400. Provided the bike has a title and a bill of sale its no problem. Shipping to the port will be about $400. Customs clearance cost little just 5% vat no duty.