2013 Cummins ISX engine. 400 or 450?

[rraccerr]

Hello Team!
Yep it’s me again with this weeks question that describes me as (Dumb dumb)
Well, I was looking at the motor to inspect leaks or problems that would need immediate attention.
And I discovered that the head cover said that the engine is a 450 Cummins ISX. WHAT!!?
It wasn’t my original cover and I just had the engine rebuilt last October. So taking it back to mechanic today after all this time, he tells me That my engine block was damaged and he Put in a 450 block. News to me. So yeah I can get in his face and scream engine murder and just get to swingin because I was told and shown my engine from machine shop was not damaged. So what the?
Now I would like to really find out if this is truly my 400 block and original head. The serial numbers found on the block match my pictures but I see you can remove them and possibly swap them to another engine so I beleive this guy can’t remember his work.
But I need to sleep tonight knowing I can find numbers on engine block and head to get the story sorted. If it’s just the wrong head valve cover, how do I get a original one , because he doesn’t have it anymore.