Wild harvested Mack AC exhausting problem

[Great White]

Greetings all: The battle rages on with the wild harvested 1926 AC.  The exhaust manifold looks to be retained by two large clamps. We would expect that if we remove the bolts in the center of the clamps that retain the intake and exhaust manifold it should come off.  It acts like there is another bolt bolding it on.  The 1924 parts book does not show any other clamps or exhaust manifold mounting bolts. It moves a small distance when pried from the front. Could there be fire rings in the ports holding it to the jugs?  Any wisdom would be greatly appreciated.