Hi. im pritty sure you will find all your problems were down to egt's.
I have seen and done this a few times. normally either too much timing or not enough fuel couses this. If you look at the exhaust blades properly you can see that they have been melted, and the same goes for the manifold. although ideally you shouldnt use a divided manifold without a divided housing. i have also seen dented blades from foreign particles, eg, spark plugs ect entering the turbo or metal objects. and they normaly look like they have been hit, but not like this.
Either your fuelling is/was inadequate or something very similar.