right guys whoever called it being the 239 lump got it right... but to be precise it is the 1939 Merc 239ci unit and is identified as such from the core plugs in the sump rails and the triangle / circle / trapezoid shape in the face of the block there is a raised 99 on the block which denotes this as a 1939 engine.
i have registered on a v8 forum.... these chaps are to v8's what you guys are to carriers!
here is a link to my query thread
http://flatheadv8.org/phpBB/viewtopic.php?f=6&t=2171