As I mentioned above, the alignment rings can cause issues. When I did our '40 this spring the machine shop resurfaced the manifold crooked. I had to make the alignment rings off center some to allow the manifolds to fit against the head. The carburetor did sit somewhat tilted towards the valve cover. Once I had the alignment rings surfaced down so the manifold would sit flush against the head I installed the gaskets and tightened it from the center out as others have mentioned. I ended up having the carburetor spacer machined a couple degrees so the carburetor sat level. I'm still not happy with the manifolds be machined wrong but I had to live with what I had to get things going. I'll change it out at some point. It ended up working and running good. Don