So I'm putting my reman back together and I suddenly realize I have a new mounting hole in the top of my center Iron. The hole is tapped and appears to be open into the engine (arrived taped over). I checked pics from my dissassembly and my old engine didnt have this hole. What's it for and what is the best way to seal it off?

 

That doesn't go into the engine, just leave it be. Usually that hole would be for mounting the egr valve on a 2nd gen and there would be a passage through the housing there for the exhaust gasses to pass to the egr valve.

 

OK, so they used a 2nd gen center iron? where is the passage in the housing for the exhaust gasses to pass and do I need to worry about that?