Have the heads or block been milled? That would make the manifold sit higher in relationship to the heads, and may bind the manifold on the studs which are on the bias. If you mill either, you should mill the manifold flanges by the same amount divided by the SQRT(2), or 1.414 for a 90* motor, and by 2 for a 60* vee motor.


Not responsible for advice not taken...