i just fixxed a 351 doing the same thing the owner took it to garage and they told him it had a cracked block i pushed it in my garage pulled oil plug and added water and the water ran out the oil plug i went to start to pull the motor and when i reached for the motor mount on drivers side my hand got wet so i started looking around and there was a small pin hole in the frost plug rite above the oil dip stick tube hole in the block that they never plugged off when they put the front sump pan on the water followed the block rite down and in the hole and never left a podle on the floor i still had to pull the motor to install the frost plug but at least it was only a 2 dollar part
What billrogers posted got me to thinkin............when you pull the intake again, examine the intake valley walls. This is where many Ford blocks usually crack when the water in the coolant jackets freezes. Usually a lateral crack (running lengthwise of the block)
