Manifolds

Not terribly hard if you have long (or several) 3/8" socket extensions and perhaps a U-joint (forget). Definitely follow the re-assembly instructions (find on slantsix.org website). The triangle and cone washers must face the correct way to avoid the exhaust manifold later cracking (opposite of common-sense), and don't lose them since hard to source replacements.

I've tried different methods to align the 2 manifold and to the head. One time, I bolted them together (3 bolts) off-car, with faces pushed against a flat optical table. Simpler is to just snug the bolts and nuts little by little, to both manifold and together, so both manifolds can slide a bit to align as they mate. Need finesse to not get an exhaust leak at the top of the exhaust manifold.

If the heat-riser valve is hopelessly rusted in place or the plate gone, you can just remove the carcass and block the holes with nut and bolt at each hole. New cars don't have that kludge, though exhaust cross-over heat is needed with a carburetor in the frigid North. I hope to eventually have EFI on my slant. I wouldn't use a long bolt across since tightening it could crack the cast-iron. I used stainless with captive nut (grooves underside to grab). Best if the bolt head is on the inside, so if it loosens it is long enough to not fall into the exhaust pipe. Always fun removing the 2 exhaust flange bolts if rusted tight. I re-installed with stainless bolts, lock-washer, and copper anti-seize on the bolt threads.