I'd have to wonder at its previous life.
My new 261 had come froma truck that hadn't run in 30 years. The whole intake manifold was full of mud wasp nest. FULL!
I had to soak it in water for a couple days to get all the mud out of it. I'd hate to see what that would have done to the motor IF I'd just tossed it in the truck and started it up!
If I were you, I'd drain the oil, flush the radiator and the block. Pull the intake/exhaust manifold rocker assembly and the head and replace these gaskets at the least. They are sure to fail in short order if they are really 40 years old. I just did the head gasket on my 216 as it leaked like a sieve after I'd run it for a couple hundred miles.
Jeremy
