I like the high temp silicons, but anything made for high temp will work.
Clean the manifolds and head really good, use a DA sander or Scotch Brite pads, anything except a grinder!
Is the gasket between the intake and exhaust still good? or is just the one between the block and the two manifolds?
To change both, start by removing the three bolts holding the two intakes together, go slow and easy so you don't snap one off. Having the engine hot helps, sometimes, so does soaking them with solvent for a few days. Once apart, clean both surfaces and replace the gasket with sealer on both sides, do not tighten the bolts all the way yet.
Place the new block gasket on the head studs with sealer on both sides and hang the manifold. Start in the center and tighten bolts working outwards alternating side to side. Once the manifold bolts are snug, tighten the three that hold the exhaust to the intake, then finish the manifold to the head bolts. It sounds like a lot of work but really isn't. Holding the whole mess in place while starting the first few is the worst of it.
Joe
