We should not overlook the disadvantage of PM alternators. At higher operating speed, the not used output will have to be dissipated. This is the main reason why automotive alternators are regulated by the exitation system.

FWIW.

        If you select a shunt regulator, you are correct, but you don't have to use a shunt regulator. You can use a switching "buck" regulator. As long as the raw stator output voltage does not become "insane", like 600 volts, a switching regulator should work just fine.

They have a 40A unit.  The hole in the rotor is sized for a 1", 10 spline shaft.  That matches the shaft from my sun gear exactly.  Now the only question is if there is enough room on the spline with the PSRU installed for the rotor to fit between the flexplate and gearbox housing.  The generator is only 1" high, so I don't think that is a problem.  It is rated for 2800RPM, but it is a small thing to rewrap the coils to give more current and less voltage.

        No need to alter the coils. (This is a lot of work.) If the rotor will stand 6000 RPM, then the alternator will work just fine. The standard voltage regulator that comes with it might not like the extra input voltage, however. It is no big deal to (for me) to build a voltage regulator to take higher input voltage, if this turns out to be a problem.