Our `Cuda used to do this. Is your battery relocated to the rear?

The only thing that fixed our hard re-start in heat issue saw to install double 00 positive and negative battery cables. We cleaned up all the grounds as well by having them all end up on a copper ground strap that led to the negative battery terminal, no grounds on the body. When the battery is fully charged, she cranks right up even after driving around the race tracks in hot weather.

"I agree check this"!

My 67 did the same thing added a ground from motor to frame she starts up right away!