Leroy Somer Automatic Voltage Regulator R449.
It can be used on LSA52.3 and up Leroy Somer alternator frames, mainly used on SDMO, Kohler, Waukesha, Olympian, FG Wilson & Caterpillar generator sets.
Other Partt Numbers:
Leroy Somer AEM220RE033
Leroy Somer AEM110RE010
SDMO 330410100
FG Wilson 954-233