Restore49
Just did a little more digging on the Cub parts site. The complete engine number for the 1641 is BS-303447-1147, the number for the 1440 is BS-294447-1145. The replacement short block for both is the same, part # BS-494054. According to the info you provided, both the 294000 and the 303000 series engines have the same bore size.
Something is different between the two according to the complete engine part numbers but I can’t find anything that would explain the HP rating difference.