F53 460 Engine runs very poorly when heat soaked

That vintage 460 and 454's ran hot. I would listen carefully for exhaust manifold leaks, they dump a lot of heat into the dog house and can affect the components mentioned already. Can you hear a slight ticking sound? Does your foot get hot next to the doghouse? Unless you have thick ign wires(10mm or so) this heat can cause these wires to leak and arc to ground. Headers will solve cracked or leaking exhaust manifold problems, add more HP and torque and make for a cooler running engine.