It is a 120000 series engine
So go to the B & S web page / support / manuals and type in 121312 - 0145
Should bring up the IPL & owners manual
03 = 2003
08 = August
06 = 6th day
FE = factory ID
B & S do not use actual serial numbers .
That way no one actually knows how many engines they made because their is no sequential numbering
OTOH that also means you don't end up with a 26 number long serial number .