Didn't the Argosy (of all aircraft) actually have self-sealing tanks, in contrast to the Herc?
If so, why the difference, all those years ago?
The Argosy's wing was derived from that of the Shackleton which in turn used the wing from the Lincoln, which was a modified Lancaster wing, which had its own origins in the Manchester a medium bomber design from the late 1930s, a time when integral fuel tanks were unknown.
The Hercules wing was a clean sheet design from the late 1940's early 1950's.