When playing the heat riser game, try tapping it left and right just to get some movement. Don't be stingy with heat or blaster, but also be careful and patient. On one of mine I ended up putting a lot of heat on it, red hot, before I freed it up. Did this with manifold in a vice. Although I have never found one, there are supposed to be shaft replacement kits that have bushings and new shafts.
To do a total complete restoration of the exhaust manifold, you need to separate it from the intake, clean out all the threads, have it surfaced flat, repair the heat riser and replace the bolts and studs. No one of these things is all that hard to do, you just have to be careful not break any cast iron. Follow the manual instructions on reassembly to the block, has to be done in a sequence.
