Look at the state of this,worse than it looks on the photo.

The new head N/S torqued up,didn't seem anything wrong with the old one.The O/S head is ready for lifting off,this must be the one that's blown.Notice the brownish colour on the O/S and all the tappets are dry.Is this the cause of the overheating problem.

We're the heads warped

Expect the gasket to be blown on 6. Check the block with a straight edge. You sticking with original cam and lifters?