1. Check the ignition timing, and make sure its not too far advanced. Also, look at the distributor's centrifugal-advance mechanism. Make sure the it is not rusty and moves freely. Sometimes, if it get stuck in the 'advanced' mode, hot starting can be difficult.
2. Consider a new starter. These starters are right beside the exhaust, so they get hot. When hot, the electrical resistance of the copper windings can increase, causing an excessive electrical load, slow cranking and a hanging soleniod.