Ford Mercury Truck Engine

[bobH]

To be clear, NO Ford trucks ever used a Merc engine from the factory (in the flathead era).[/QUOTE]

I'm nitpicking here... might want to check that comment. If "trucks" includes pickups, I believe there are some exceptions... It's been reported here that in the 1940 era, it was possible to get a '99' engine in a truck. (I can't verify.)
This was reported to be verifiable by a unique frame id number.
Then, in the 46-47 era, trucks came with a 59 engine. And, we all know that 59 is a 1945 MERCURY part number prefix.
It might be more appropriate to say that no V8 FORD, in the 46-47 era, came with an engine identified with a FORD part number.
That changed in 48, when V8 trucks came with an 8BA, which IS a Ford number. Maybe 48-up is what is being referred to???
IMHO

[Ross F-1]

The context of this discussion is 239 8BA and 255 8CM engines. So yes, 48-53.