For what it's worth, "Ford Army parts Catalogue 1940-1942" SE39-42 reissued January 1942 lists all CMP Fords from F8 to F60H as using RH manifold 78-9430 and LH manifold 78-9431. No differences listed for weight of vehicle or number of driven wheels...
Here are links to a couple of previous MLU discussions of right hand Ford manifolds.
http://www.mapleleafup.net/forums/showthread.php?t=23472 http://www.mapleleafup.net/forums/sh...ad.php?t=11790
A quick google on the part number came up with several that seem to be for sale.