I'm still pretty green to the mopar world and now I just bought a '66 Polara. It needs some TLC but need some info on the motor. It apparently had a 440 Big Block which was trashed and now has a 318 Big Block. I've never heard tell of one but are they any good and can you make decent power with them? Thanx for the info guys.  

There is no 318 big-block. It's likely a polyspherical 318. These engines can be built to make decent power, but a 440 would be the logical swap.