[Woodz428]

I have decades of experience with virtually all FE size engines, in the same confines there shouldn't be any signicant temp difference. I can see how some of the 390 blocks that have been bored to a 428 bore might run a little hotter, but a factory block? I don't think it should.
You also have to keep in mind that HP=heat, so the more power that you want to get will create more heat to be dispersed.