HAH! I got my car with 250k+ on the stock '85 motor, and to my knowledge (which is at least from the previous owner) not even the valve covers have ever been taken off. That being said, my car has a previous best time of 14.7 at 98mph, and that's before the mods in my sig, and that's literally only 2 months before i aquired the car. Since then i've put at least 5k more miles on it, plus all those mods, but i have yet to race it.
Hey, i dont doubt that i'm on borrowed time with this motor, but at least it's still kicking some serious arse. I'm doing a compression test as soon as i can get ahold of a gauge, but i expect it to be pretty good.
As for the Cobra, i agree that's a high price for that many miles, but mileage is only relevent to collectors IMO.