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

Sounds like intake and heads milled at different angles, for sure....

How about this....properly torque down the intake with a new set of gaskets(no sealer!)...let it sit a while (overnight?)...then remove the intake, then the gaskets (carefully) and "mic" the top and bottom of the gasket intake ports . The difference in thickness should give you an idea of the angle difference...ballpark figure at least.