On the big blocks I've seen 2 kinds. One is very thin where the manifold goes over it. The other is thick like 3/16 where the manifold goes over it. The picture looks right to me for yours. Just by looking ?
That is the exact gasket that is shown in the picture. It is the Dynamite >.21 gasket. pretty much any gasket for .21 and over engines will fit the Mach .26.