Dom et al,
I have received several suggestions on the 460 and Big Block Ford web sites that I'm going to try - well, at least two of them.
1) Add a separate solenoid away from the headers on the firewall. Here are a couple of links to give the wiring:
Adding a Remote Starter Solenoid to your Chevy, My Way
(Ignore the mention of the Ch3^, it uses the Ford part) and
Starter goes click-click when hot - 460 Ford Forum
Still not sure why the solenoid helps, but several knowledgeable folks have endorsed that approach.
2.) I think I'll try a heat shield along with it for good measure.
A friend once said about my approach to a problem was "when you see a problem, you just start throwin' hammers" LOL
Tom