I found this on a dodge form and thought of your problem. I am having problems with my V10 and I think it is a head problem. It does not hold radiator pressure any more and is burning 1 gallon of coolant in 1000 Miles
But here is the info I found
If you still have a 318-360 magnum engine, and it started to use alot of oil, they have a problem with the plate thats bolts to the bottom of the intake manifold. The gasket blows out in between 5 & 7 cylinders, and sucks oil out of the lifter valley.