Possibly intake gasket or manifold gasket as 461 said, upload some pictures of how milky it is... What RPM were you hitting when you took it out? How long were you in that rpm range? Was the oil milky prior to you taking it out?
On an olds it's very nice to have a water pressure gauge on top of the intake so you can get water pressure dialed while keeping an eye on the temp guage...
I run 5 psi at 3000 and 12 psi at 5200, while staying at 150 degrees cruising and 170-175 at idle..
Sent with my Fingers