Good old heat soak...
1/ Wrap the headers in heat wrap tape at least a foot in front of the starter and six inches behind the starter. Make it a double wrap thickness and secure it with hose clamps or wire.
2/ Replace the primary starter cable with a #2 cable, making sure it has totally clean connection ends.
3/ Replace the ground cable between engine block and battery ground, again, make sure contact surfaces are really clean.
4/ Check and clean all other ground cables making sure all connections are really clean.
5/ Double check battery charge rate is at least 14.2 volts at the battery itself with the engine running around 1500 rpm.
6/ Check static timing and set at 8 degrees at idle,,,idle being 650 to 700 rpm.
7/ If above fails, replace starter with small format reduction gear style starter that also has a heat shield built into its design.
Above all...have FUN !!!!
