Intake manifold won't seal - How do I check it ?

I have an update. I took the measurement that EL5demon got for me. I measured my intake and came up with 48* on all 4 corners just like he measured. So that means the intake will milled to the correct angle.
I noticed a dark outline around the heat crossover port on the intake, but it was off centered a some. I sat the gasket on the intake and matched it up with the heat crossover outline. I noticed how the gasket sat very low on the intake. So I got in some better lighting and looked a lot harder at the gaskets. I can see the outlines very well toward the top of the intake and I looked toward the bottom of the gasket and that is when I saw what I think was the problem.