I hate having my first post not be an introduction, so forgive me, but I'm in a bit of a tight spot at the moment. I recently bought an out of state '14 370Z with Megan's Racing headers and test pipes. I decided to return it to stock for CA emissions hassles not being worth the minimal gains from short headers and test pipes. After spending a small fortune on the OEM exhaust manifold and cats, I pulled off the currently installed headers and have ran into a situation.

I got the headers off and found the OEM manifold holes don't line up with the holes/studs in the head. By not line up, I mean on two of the three cylinders on each side the holes are in opposite corners of the cylinder. After watching a ton of YT videos, it appears that this is very normal. My issue is it seems like the previous owner filled in the holes in the head the factory manifold used.

Any ideas what is filling the holes or why they would be filled? Any idea on how I should move forward? Any chance this is an aftermarket head and it was made that way?

My first idea was just paint and wrap the Megan's racing headers, then bolt the factory cats up to that, but the flange on the headers don't match the flange on the cats. I could have someone cut off the flanges and weld one on to the other.
Another idea I had was pull the head and drill out whatever is filling it. I would rather not do that myself as it'll take me another 10 weeks to do it (I'm not a pro and everything takes me 10 times longer).

Thanks in advance for any advice.


Drivers side.

Passenger side.

Close up of the rear cylinder.

 

I think I figured out a solution. After actually looking at the flange on both sets, I realized the middle cylinder had 4 holes so I only really needed to move the studs on one cylinder per side. I think I'm going to drill a hole where the red circle is and then weld a little steel and drill a hole where the yellow circle is. I don't weld, so really I'm going to have my exhaust guy do that part. He said he didn't think he could weld and then drill it and we might have to punch that hole with a plasma cutter. May not be the prettiest, but that is a lot better than pulling the head so it can be drilled out only to find something else is wrong that is being covered up.

I'm still curious about why the OEM holes would be filled in. Let me know if you have any ideas or see any issues with welding and drilling the flange on the manifold.