The main differences are the emmission systems. The US bike will have the evaporative canistor fitted and pipework and a different ECU. It'll still work, but not quite as well as a euro bike.
It can be removed and the ECU swapped/reflashed though.
Headlight is the same so no need to go swapping that out.
You'll need to get the paperwork sorted for UK registration and i'm sure there'll be a cheque going off to HM tax collectors as well.
I'd get all that worked out before deciding it's a bargain, just to be safe