I actually did a lot of dimensioning and stuff of the original manifold and I didn't see anything like that. The hole between the two center cylinders and the slot on the back cylinder is actually smaller than the rest of the holes. I actually had 1/2 inch dowels in all of the large holes and then it was clamped to an angle block and they all seemed to be within a matter of a few thousanths I would say.

This model should be pretty close dimensionally to the original manifold that I have. I would even say that a lot of the features should be within a matter of .02-.03 thousanths of an inch or even better.

Some of the stuff though I did kind of go by feel. Mainly because I am running out of time on this project. I only have about 2 1/2 weeks until it should be for the most part done. But then I have about a month until I have to present it to the class. My teacher wants us to focus on the presentation for that last month. Though it doesn't mean though that I can't work on it some more.

But I was going to make a grey iron casting pattern model, 3D print some parts, figure out costs and materials, production, ect. ect. Lots of stuff to do yet so I do need to move forward I could come back to some things though.

 

Well it looks like the presentation will be good. However, if you do coonsider production, it will be worthwhile to determine the exact location of all of the holes. That way you can make the best use of the space available for the ports.

Here is a 2d drawing I made of a felpro exhaust gasket. You can see the offset I speak of. I can even send the cad file for it. I drew a line between the centers of the end holes to make it easier to see the offset. I have also verified this by comparing it with a head.
In my drawing, it's .089" offset which is just under 3/32.