[BB427]

One thing to check is the plate on the rear of the water pump. On the FE engines the water pump is a self contained unit somewhat like a chevrolet (sorry) On the 429/460 there is a plate between the water pump and the timing cover. If this plate is not in place the water pump just cavitates and doesn't move any water. Also as Tom said make sure you bleed the system well. I added a braided steel water crossover tube to the rear of my intake from head to head, it did help and allowed me to bleed the system in another area.

Good luck!