I don`t have a Blue Thunder intake manifold, but I just finished up on the 428 CJ for my 59 project, and had a similar experience with my Edelbrock Performer RPM intake. I used the same stiff blue FelPro intake gaskets, and 1020 head gaskets, and when I test fitted the Performer RPM, I could see that the intake was sitting too high, the lower section of the intake was resting on the exposed area of the head gaskets that stick out between block and heads into the lifter valley. I just took a hammer, and carefully bent the edges of the head gaskets down, over the top edge of the valley tray. Doing this allowed the manifold to sit down lower, and allowed a thinner bead of sealer to be used on the China walls. Last Thursday we did the 1/2 hour cam break in process, and then made 6 dyno pulls, and the intake was dry everywhere, with no smoke, so I have to assume the intake is sealed up properly.