TM454, just a a little clarification, the 400 only had problems overheating when the wrong heads were mated up to it. The siamesed cylinder bores would generally need a couple small steam holes drilled into the block beside them (into the water jacket), and the gasket would have to be clearanced to match up with the new holes. This was to prevent steam pockets from building up and overheating the block.
I have seen many 400s run at normal temps. Some had this mod done, and some didn't.