I managed to get the manifold flange detached from the manifold by cutting the bolt/nut ends off with a metal cutting disc, then loosening the bolt shafts by wrenching the bolt heads....not easy or fun....to get to the inside bolt I had to squeezle under the truck and reach up alongside the engine block. I then discovered that my acrobatics were unnecessary, since the inside flange ear of the manifold was cracked right off.... I then looked closer and found that the rear/outside ear was almost cracked through, leaving only one good ear of three. I can tell that someone long ago had had this apart because the jam nuts on the flange bolts are not all the same. This leads me to believe that someone tightened the connection way too much AND/OR the GMC engineers made a little goof in deciding how thick to make the cast flange ears. What to do now? Removing the rear portion of the exh manifold is a possibility, and weld it, but something tells me that cast weld would not hold up to the retightening.
