John:
If your motor was honed with deck plates (if it wasn't, find a different engine builder), your rings should be seated within 100 miles. I would wait for 500 miles just to be safe. I personally don't think its worth the leaks that it will inevatably find in your engine. Unless your engine is perfectly sealed, it will find the smallest crack to get out of. Don't get me wrong, I would use it in a factory built engine that I plan to keep for 100,000 miles or more in a normal type street car, but I doubt you will ever see more than 30,000 miles or so in a Cobra. Even if you plan to put more miles than this on your replica, changing it every 2,000 miles or so with regular
oil will make it last forever. You might say: but what about the 15 or 20 HP I will loose with regular
oil? Does 450 HP vs. 465 HP really matter?