What kind of generator is that- it looks like the field coils and armature are fed in parallel from Batt(+) and the current limit opens the high side armature/field feed while placing resistance in series with the field coil low side return to GND. The low side of the armature is permanently connected to GND. It looks like the old time current regulators routed a portion of the field coil current through the armature current sensor magnet for hysteresis. Your circuit proposals are shunting the armature current away from the battery and doing nothing to limit generator output. Part of the current limit is to protect the generator against overcurrent and your scheme does nothing about that. It would be a shame to burn up that relic. You can use an LM185 to make a precision high side current sensor if you want to stay away from GMR or Hall Effect. But this isn't going to do you any good unless you use it attenuate that field coil current.