Why would antifreeze be in the oil pan of a ford 351m engine?

You either have a cracked head gasket or a cracked head or a cracked block YOU MAY HAVE A BLOWN HEAD GASKET OR A CRACK EITHER ON THE ENGINE BLOCK OR CILYNDER HEAD. YOUR OIL HAS CHANGE TO A MILKY WHITE SUBSTANCE RIGHT? IS THE CAR SMOKING? Yes it smokes like a freight train.I RECENTLY REBUILT IT AND PUT AN ALUMINUM EDELBROCK INTAKE AND CARBURETOR ON IT. I HAD THE BLOCK CLEANED AND BORED 40 OVER AND ALSO HAD THE HEADS SHAVED.COULD IT BE THE INTAKE ? IT SEEMS TO ME THAT AS FAST AS IT GOES INTO THE OIL PAN IF IT WAS A PROBLEM WITH THE BLOCK OR HEADS THE SHOP WOULD HAVE SEEN IT. THANKS FOR ANY HELP YOU CAN GIVE. TRY CHECKING THE MOST COMMON CAUSE WHICH IS THE HEAD GASKET. TRY THIS TEST. IF IS A V6TYPE ENGINE TAKE OUT MIDDLE SPARK PLUG ON 1 SIDE ONLY, AND HAVE SOMEONE CRANK THE ENGINE.(JUST CRANK IT A FEW TIMES OR START IT FOR A SECOND ONLY)YOU SHOULD BE ABLE TO SEE THE "SMOKE" COME OUT OF THE SPARK PLUGS HOLE. IF NO SMOKE, GO TO THE OTHER SIDE AND TRY THE SAME TEST . ONCE YOU FOUND THE SIDE THAT IS HAVING THE PROBLEM ALL YOU NEED TO DO IS BEGIN LOOKING FOR CAUSES.(''IF YOU GOT SMOKE ON '''BOTH''' SIDES THEN THE PROBLEM MAY NOT BE THE HEAD GASKET ,VERY RARELY BOTH SIDES GO BAD AT THE SAME TIME'') SINCE YOU SUSPECT THE INTAKE ,HAVE A LOOK AND CHECK IF IS SITTING PROPERLY IN PLACE AND THE GASKET IS IN PLACE.BUT NORMALLY 99% OF THE TIME THE HEAD GASKET IS TO BLAME. NOTE.COOLANT USUALLY BURNS OUT IN THE COMBUSTION CHAMBER ,BUT SINCE YOU HAVE FOUND IT IN YOUR OIL PAN YOUR PROBLEM MAY BE A LITTLE DIFFRENT/COMPLICATED.YOUR PISTON RINGS ARE ALLOWING IT TO GO DOWN IN TO THE OIL PAN WHICH IS SOMETHING THAT HAS TO BE ADDRESSED AS WELL.