Hi. I notice you've had no response to your post, and I suspect it's in the wrong forum. The Planning Forum, as you can see from the description, is about 'Where to go, when, what are the interesting places to see.'
To increase your likelihood of getting a response to your questions, I would take a look at the other forums on this board, and post separately on them. For example, your question about 4WD preparation should go into the 4WD Travel Forum, which covers 'for NON-Sahara specific subjects, 4wd TRAVEL tidbits, technical discussions etc.' Your question about safety across West Africa should go into the Sahara Travel Forum.
I can tell you that it will likely be prohibitively expensive to ship a land rover across from the USA to UK. For reference, it costs about $1,000 US to ship a motorcycle.
Good luck with your trip!
"It matters not what goal you seek
Its secret here reposes:
You've got to dig from week to week
To get Results or Roses."
'One world, two wheels'