I bought a 1953 chevy 1/2 ton parts truck that had a lot of oil in the radiator like you describe. When I took it apart, I found the copper tube that goes from the bottom of the engine to the rockers had been routed between the top of the block and the head. Of coursed this "squished" the oil line and let the oil flow through the water jacket. I replaced the oil line, flushed the water and it ran nicely. I don't know if your motor has this oil line, but strange things happen to these old machines. Good luck!
