I just want to make sure I am clear on this since there are two wiring diagrams in the instructions (nice work on those BTW) but they don't indicate coil specs with and without the ballast and there are conflicting answers online.
When you suggest a <1 ohm coil, do you suggest that with a 280z ballast such that the overall resistance is roughly 1.5-1.8ohm? Or just the <1 ohm coil?
I believe you don't need any ballast with the HEI module because as you have stated, it limits the current so there is no need for a current limiting resistor. The Pertronix D2000 Flamethrower module limits current to 6.9A. The 280z stock setup should be 6.6A (12v/1.8ohm) so it isn't a huge upgrade which is why keeping the stock ballast/coil setup in a 280z could be just fine.
My current planned setup is 260z distributor, Pertronix D2000 HEI module, Flamethrower II coil 0.6ohm, no ballast resistor. Jump the two wires currently on the ballast so my tach still works.