The 29 was also manufactured throughout WWII...by us, the Canadians, and the Germans!
USA ones are not marked on the block; the ones used on Mercs had heads that say 29A, but those fit on any 24 stud...you need to pull heads and post pics of manifold area and deck surfaces to verify what the engine is. Also MANY 29's were in civilian trucks (no 29A heads) and on military vehicles and so lacked even the head cast 29.
Too much has happened in the last 70 years to trust any flathead identification based on removable parts!