This is odd to say the least. I know on oldsmobiles at least there are water passages on both sides of the intake. It flows through the block, up into the heads, through the intake and out. I think. Its possible that your head cooling ports are where the water flows out and through the thermostat. that would explain the front-only flow. As for your bearing problem, if you already have the cam out, i would check your book for any pictures, then check for a hole on the top of the bearing. Its possible it was put in upside down.