The cars have generally proven to be quite reliable. There was one member on here who had about 185,000 miles on his a couple years ago, and he reported that he had no problems at all with the car.
The engines were used virtually stock in the Formula Ford racing series, which gave me a good feeling about their durability if they can stand up to the demands of racing.
I hope they don't rust out, that's what happened to the Capri which was the first performance Ford I had a long time ago, and which is the source of my forum name.