@John767 let me get this right,
you are thinking of flying best part of 300 miles south to buy a £875 car that the current owner traded in a month ago.
The car has been modified for drifting and has a welded diff.
You are then going to drive this car 300 miles back north, having never driven a car with a welded diff.
Well, I'm always up for a daft challenge and having driven a fairly well sorted 150bhp Chevette with a welded diff on the road, have a rough idea what it'll be like. Honestly, you need your bumps felt mate!
If you manage to get it home, the cost of getting it and a diff swap make it not worth it. If you are involved in an accident I'll bet your insurance will be very much void and I bet they won't insure you if you declare the diff.
Keep looking....