These charts may help visualize how these sets were distributed and used.  I wish I knew what doc they came from, and that I had better scans.  Maybe someone will recognize them and be able to share a better copy.  It's possible the original is buried in my files...

As another data point, my friend's father, PFC Joe Rapp, carried an SCR-300 as a USMC field radio operator during the battle of Okinawa.  His battalion had 4 of them, one for Headquarters Company, and one each for Companies A,B,C. 

USMC doctrines and gear are, of course, going to be different from US Army.

RF