Sounds awesome Bubs
When i started playing with my set up, which is similar to yours, i was using way higher voltages on my alternator, like 30 volts, then i clued in that i shouldn't go over 12 volts on the variac, and then i clued in that Stan only ever goes up to about 5 volts on the variac.
Don, so there are 4 layers, back and forth along the core, with cardboard in between? in your first description i was imagining the card board made little bobbin cavities like on the vic coil, so it had 4 spiral sections.