I had a similar problem with my 350 in my 49 Chevy car. My battery was mounted in my trunk. It would not start when hot, but started great cold. I tried the wrap around heat shield (be careful not to let it touch the hot wires tot he starter when you wrap it around there. It did not work. I fabricated a shield that clamped to the exhaust pipe to shield the started, did not fix it. I found a kit that Painless wiring offers for Chevy "hot start" problems. It basically just adds a F@$$d solenoid between the battery and starter. This has worked like a champ for many years.

Kevin
http://community.webshots.com/user/49chevyman?vhost=community
"The only people who do not make mistakes, are people who do not do anything."