Hi Brendan,
What is a guy in Cleveland looking at UK cars for?
Looks like that price is a little steep to me. Roughly CDN$10,000 for a car that is still in primer. If it is a GT500KR or a GT350 I would look more seriously. Also if the only thing it needs is paint, and the rest of the car is a professional, ground-up restoration, it might be worth it by Canadian price standards. However I suspect it will be a lot like Australia and prices will be through the roof on American steel. Also keep in mind that running petrol through the thing will leave you broke, never mind the additional insurance, and you will never be able to afford an HI Khukuri again. Count on 13-18 miles to the gallon (~4.5 Litres), depending on which engine you get.
Not knowing what UK prices on American cars are supposed to be, perhaps you could pick up a couple of trade magazines or advertisement magazines from the same part of the country. We have something called the 'Old Car Trader', a weekly newspaper called the 'BargainFinder' and weekly publication called the 'Auto Trader'. All are good sources to cross-reference prices, and I suggest you do exactly that for a few months or even years, before jumping in and buying an old Mustang.
Just sold my '70 Chev Custom Camper Special. It had 68,000 original miles on it, a big-block 310 horsepower 402ci and is beautiful. I needed the money, and never drove it anyway. She has gone to a family that will treat her with great care though. A good home for her. Nevertheless I will miss her...
Notwithstanding, buy a Kothimoda Katana, save ~3700 pounds, and be very happy instead. There are at least a dozen ways to satiate a lust for beautiful things.