Very interesting. Was the top open channel water jacket? I recognized
the lower one as the oil gallery.
I'm curious as to the events that led up to the thrown rod and exactly what
separated. Looks like maybe the rod cap came completely off. So was it a
failure of the rod cap bolts? Where is the 13mm measurement on the later
rods that you mention?

My closest experience to this came to a head in San Simón, Arizona on I-10
just west of the NM state line and was the result of a lifter/rodcap bolt
impact on a B30F after changing a cam without pulling the engine. Apparently
one of the errant lifters that I failed to catch got down somewhere near the
fuel pump boss and hung up and was later hit by #2 rodcap on a hard corner.
It was a sickening clank but no further symptoms for about 3000 miles.
Eventually it started knocking, getting worse rapidly and dropping oil
pressure. The engine pretty much gave out before it let go completely
but when we pulled the head the top of the piston under the flat surface
of the head as well as that mating surface, was VERY clean and the piston
was TDC. Son in law reached in and touched it and it dropped about 1/4"
with a clank. Probably could have been fixed but I lived in Panama, we
were at his house in Yuma, and he was leaving for Korea in a few weeks, so
we took off what we could and sent the rest to the crusher.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma