Hi,
Yes, E38774 is a part number for a coolant connection on some RR Merlin engines, probably on the pipework feeding the cylinderbank connections. Unfortunately, I do not have a parts manual for the 45/46 etc series that would have been on a Spit V, and the later info I have shows that part E.38774 was superseded by RR Merlin mod.2157.
Eng