The '41 engine has flat top pistons and the '39 has dome top pistons , so the heads are not interchangeable , also the '39 has a different rear main bearing , so you would need to find a complete engine if changing years.

Just how bad and where is the crack ?

I have been driving my '40 with crack in lower water jacket for 20yrs . Still just keeping an eye on it.

edit , yes the '41 - '46 are the same.

Last edited by Dusty; 04/01/2017 9:34 AM.