I use to have a 460 and I always had a hard time with starters. The Ford needs alot of juice to turn over and I would have to replace them every few years. A dealer told me to have a high torque starter built and to use the biggest cables that I could find. A place called Holt auto electric in Ontario CA.was where he told me to go.
Just a hole in the wall place but the one they built lasted 12 years, They built it to marine specs. since I had an enclosed engine. I think it was about $80.00 or so.
They are in the phone book