was this block oversized at all? was it honed or machined in anyway b4 u installed these new cosworth pistons?

 

It appears that your wrist pin to small end of the rod were not mic'd for proper clearance on top of whatever your other issues are.

 

Need picture of sides of pistons looking at ring lands. You got all kinds of wacky angles. all ring land pictures are blurry. all I can determine so far is there was no scuffing on skirts. a couple of pics show possible detonation but are too blurry to tell. there is considerable darkness between lands for that mileage also supports this. if the top of piston is over heated from detonation it can pinch top ring from floating and score bore. then all ring seal would be shot. how do bores look?

 

I would highly doubt that cosworth pistons are not checked to spec before they are boxed...