This is a newbie post...I just recently purchased a 1996 two door Tahoe.
I bought the vehicle knowing it might possibly have a blown head gasket or
cracked head. Well long story short, it was a cracked head on the passenger
side. I tore the top part of the engine down and removed both cylinder heads. This is where I found the two and a half inch crack on the passenger side head on cylinder number four. From there I purchased a pair of
re-manufactured heads from O' Reilly's auto parts store. I put the passenger
side head on first with no issues. However when I went to put the drivers
side head on I noticed a hole at the back of the engine block that the cylinder
head only partially covered. I don't know what the purpose of this is for.
It's close to the oil pressure sensor so I don't know if it is an oil passage or water passage hole. My question is should I try to plug it or get a different
cylinder head? I have attached photos to show what I'm talking about.

 

Welcome to the forum.

Would appear to me that the heads aren't the right ones.

Can you tell if the hole goes anywhere?

Any oil or coolant residue in it?

Are your old heads still available to check?