Joe,
I brought this topic up on the NCRS technical forum and heard
from some very knowledgeable, long-time big block owners
and racers ( past & present ). I rely on these guys heavily
as many of them have been around big blocks from almost the
start of the Mark IV program.
The general consensus is that all 4-bolt main BBC engines
would also have received the external oil cooling provision
as part of this SHP feature. No members reported seeing a
4-bolt main block without the external oil cooling provision
and this jives with what we have been discussing here.
Not conclusive proof, but I have learned to trust the input
of the NCRS on all topics of an historical nature.
Steve