If I remember correctly.. if the alternator is good it will cause a magnetic field regardless of the voltage regulators condition. That's how we use to trouble shoot a bad alt. or reg.

1971 duster twister 440, 3380#,509 M/P hyd,906's,full Exhaust,11.06@117.46 1/4,6.95@ 97.03 1/8,1.497 60ft.....