Wayne,
Looks like you have one too many "6's" in your number. Should be 7 digits not 8. So, with that being said, the "18" prefix denotes it as a "Ford transmission" this was used from 1932 till 1942. Mercury was "99" , Lincoln was "H" this all changed around 46 to 48.
Judging by the VIN you provided, looks like a you have a 1941 Ford transmission.
Cliff Ramsdell