Diode will only be used for reverse current, right now we are going to use a transistor switch on switch off to adjust field strength. You have got me wondering about the heat issue, just cant see that being an issue with only 20 amps especially when most of the time current draw is only in the neighborhood of 10 amps. I have a test bench made and when I get this thing on a breadbord I have a carbon pile resistor bank I'll put the squeeze to it and see how much it heats. Will keep you posted. As I said before though if heat is an issue I will leave the originall reverse current relay intact when I cannibalize the regulator. Here's one allready been done, but for an "A" system the delco's are "B" systems
http://idisk.mac.com/forever4/Public/pages/generator.htm

1965 chevy c-80 409 5-2 20000 original miles.
1965 chevy c-60 348 5-2 single axle tractor.
1952 chevy p/u 235 4 speed restored.
1965 chevy c-60 couch.
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The future is not what it used to be.....
Have a new pair of metric vise-grips and large metric hammer, can fix anything...