I've been doing more figgerin with an inductor core. This time I think I understand the process. Adam Brunette had recommended the E827 core family from micrometals.com. Specifically E827-2. I would use 6" wide copper sheet and nomex for doing a single roll that's around 25 feet long, and close the 2 E's around the roll.
I worked through all the formulas and finally think I understand the process. The core loss is very reasonable with that core. At 400amp, 144v input, at 10KHz and 100uH inductor, it would be about 35 watts of waste heat in the core. That's certainly manageable. And it's a beefcare core too. around 6Kg per half.
https://www.dropbox.com/s/wasp3nr1mt...Sheet.pdf?dl=0