Well, I tore an 8n down for the same reason
as you. Oil in the radiator, ran great, no
coolant in the oil, smoked and was tired, so
the guy wanted a rebuild of his engine.
Pulled the head off, looked good, head
gasket looked ok. Started pulling sleeves
and there was total carnage of the parent
bore of the block. Every cylinder was split
almost top to bottom. Somewhere in there it
must have made it from a cooling passage to
an oil galley in the block. Obviously there
is no oil passages in the head, so that
eliminates that for you. I was also told by
a Ford N series guy that oil from combustion
will work it's way into the coolant, making
it look like oil in the coolant. I don't
know how you would know. Maybe just with the
test strips that check for combustion gases
in the coolant? You can get those at an auto
parts store, if you have a decent one. The
owner of the 8n I was going to rebuild
decided he wanted a tractor that was a
little bigger and had more modern features,
so he decided to part his out instead of
spending money to fix it, and add the money
saved and the money made to his new tractor
fund. You may get some more help if you post
this on the N series board too, if you
haven't already. There are a lot of good
guys over there that know a whole lot more
about them than I do.
Ross