Great link, salty9. Alternators of all sizes are readily available and cheap as used. He states a custom-made permanent magnet rotor is more efficient (no battery juice used to power the rotor), but using the existing rotor does allow field-weakening (as LFP suggested) so the field strength could be tailored for max torque or low cogging drag (perhaps automatically by an electronic box, RPM-based? throttle-current based?).
"...2200 RPM. This is where the motor peak efficiency is for 1000W output power. The 1000W power level is of interest to some e-bike people..."
I've always liked the form factor of alternators, the size (and built-in fan) is good for absorbing and shedding heat. He suggests that the larger and common "Chevy truck" Delco alternator would have 5 times the torque (E-scooter?), but the Denso he is experimenting with (as a large RC-plane engine) is (in his words) half the size. He has looked a great deal for the "best candidate". Proper size, good copper fill, reasonable quality laminations, common, cheap as used...worth looking into?
Sounds like a good replacement for the 80-100 when its out of stock, 2200-RPM could mean a single-stage to a 20-inch rear wheel.