I am beginning to wonder if the sequence of events could be as follows. The first models of the P-51D did not have a hand pump. The hand pump was used in earlier P-51 models to move the flaps.
This quote is from P-51 pilots check list:
http://www.aerofiles.com/checklist-p51.html
"There is NO emergency wing flap operation provided on the P-51D, as the hand pump has been eliminated. On all earlier models of the P-51, put flap selector to desired position and operate the hand pump until it seizes. Flaps will be in desired position and will stay there until another selection is made."
Suppose that then field modifications (perhaps not "official") were made to install the Model B hand pump in the Model D because of pilot demand.
Next, at some point, the hand pump (now with model D numbers) was added back to the model D and K P-51 construction as Steve B's parts catalog seems to show.
There is also a "late" version of the P-51 D/K parts catalog that can be downloaded from here:
https://ww2aircraft.net/forum/thread...catalog.50278/
What is interesting is the section on the "hand pump" (now called part number 109-580243 which supersedes part number 106/109-580241) has a notation that the hand pump will come wrapped in felt and is stowed as loose equipment.
It will not be factory installed.
I would appear that the AAF went "back and forth" on whether the hand pump should be in the model D/K. Finally they just made it "optional" and included a pump that could be field installed if desired.
If this theory is correct, it would appear that the Model B pump bracket that was found was part of the Model D that crashed. It seems unlikely there also is a complete "P-51B" at the same crash site.