Couple of other things to consider from this side of the pond.
This guy states "must sell" and "Cash" only deal, no trades.
Just for your info, under US law, any transfer, payment or transaction with documented records (such as a check, wire transfer etc.) where the dollar amount is $10,000 or more is subject to scrutiny by the American tax man (Internal Revenue Service or as we like to call it "the INFERNAL revenue service"). The only $10,000+ deals that don't get reported to the tax man are private deals done as cash-in-hand with no documented records. If you're planning to do wire transfer of funds or the like, it might be held up by a US government investigation.
Being in the money lending business, there are a couple of US Government departments that could get involved. One is the aforementioned IRS, but the other is The Department of Homeland Security. You don't want to red-flag those guys as right now they are watching a lot of financial transactions as a result of ISIS activity. Even Americans refinancing their mortgage (where they are cashing out accrued equity) are required to sign a document permitting the US Government access to snoop around in their bank accounts to ensure the money is not being sent to terrorist groups.
Also, and so you know, there are people here in the US who often put $9,999 cash down payment on a new car (and finance the rest) so the dealership doesn't have to report it to the tax man or Homeland Security. Then they don't have to explain to the government where the money came from.
Presently, Las Vegas is the US city with the highest number of foreclosures and there are a lot of bargains to be had as home owners there try to stave off the boogie man from repossessing their homes.
It might pay for you to hop on a flight and go see the car and even try it for size. A round trip flight may only cost $500 or so and that's a lot cheaper than a 12,000 pound ($16,000) mistake.
If it was professionally built, then it should have a whole lot of documentation attached to it. It should have a chassis number or certificate that can be traced back to who built it and how it was built including the specs and possibly the blue prints. That way you would know if it can be modified.
If it is a "backyard special" with little or no documentation, then you could be laying out a lot of cash for a "pig in a poke".
Good luck with your plans