C15 cat bubbles and pressure radiator

Immediate cooling system pressurizing on engine start. Blows coolant out of the radiator cap. Apparently engine lost coolant last year and was overheated. driver filled it with drinking water asap and kept going. Put a cooling system tester on it to check for exhaust gasses and it changed colors.

Just pulled the head. All 6 cylinders exhaust valves cracked between valves. Possible head gasket blown as well. Looking for input on this. Not really sure what I'm looking at or checking for.

 

What about the cracks between exhaust valves? Showed photo to service manager and he said definitely head job? What should I be looking for on the sleeves, block and spacer plate. Nothing looks obviously damaged. Was looking for a break in the fire ring but I guess that isn't a necessity .

 

I'll print up a worksheet and go thru the numbers on it to see where we are at on liner protrusion.

 

Little bit better photo and it becomes a lot clearer.
On the rest of the cylinder fire rings you can see the gray gasket material forming a raised circle except between #4 and #5 cylinders where #4 blew out. Would anything else cause that but bad liner protrusion? Had 2 head bolts a bit on the rusty side between #5 and #6 cylinder on the passenger side.

 

Zoom, zoom, zoom and there she is. The obvious...
So, what's the best way to clean a block with the liners still in? Just scrape everything into the coolant passages and slap it together before anyone notices? any tips appreciated