!966 Impala Starting Problem

My 66 Impala 327. Will not start when it gets hot. I mean it will not even crank the motor. I replaced the starter and checked the rest of the charging system and all checked out good. If I let the car sit for 15 to 20 minutes, it'll start right up. Can anyone shed some light or send me in some troubleshooting direction.
Thanks

Very typical hot soak GM starter problem. You could fabricate a heat shield to fit around the solenoid and starter, first check voltage drop and amp draw when hot to make sure the battery and starter are good, also make sure you have a good engine ground also. Last resort they make a high torque starter also to help over come this. Timing must be set right also, of course.

What should I make a heat sheild out of? Where can I find out about the high torque starter Thanks

Most any good parts store NApa for example has these, new. Any type of sheet metal will do, not aluminum. Do the suggested checks first.

I feel that I have a pretty good ground though it does worry me some. From the negative battery post there is a 4 gauge cable attached to one of the water pump bolts. The ground shows good with a meter but I know that there is a gasket in between the housing and the block. The bolt goes all the way through so it shouldn't be an issue.