Updated: Feb 20, 2021
on all of these engines, the factory had a heat riser valve operated by a thermostat style spring to aid in keeping the engine from being cold blooded in the snowy climates these vehicles were daily driven in when they were new. few people drive these classic cars in these conditions anymore, and even if you did, it's still not necessary to leave it on the car... and the reality is the risk involved with it not working properly isnt worth it to keep it installed. if it ends up frozen shut, you can crack a cylinder head, warp valves, get hotter coolant temps, drastic heat soak and vapor lock symptoms, etc. probably 60% of the time, the valve is frozen in the shut position when these cars/engines come in here. if they arnt frozen, then usually the shaft bushing is so worn out its an exhaust leak. the 322s/264s had the valve on the bottom of the drivers side manifold. 56 and later was on the passanger side. 64 to 66 had a seperate housing for it that bolted under the manifold with longer studs. because the housing top and manifold bottom are a flat surface and the bottom has a tapered flange to mate up against the exhaust pipe, you cannot just leave the housing out entirely. frozen shut heat riser valves are also the reason why many of the 364 four barrel intakes out there have a crack along the bottom of the exhaust passage on the intake. those manifolds are very thin and prone to that crack.... so whenever you're looking for a 364 four barrel, be sure to look for that crack prior to purchasing one.
so you know that your heat riser valve is frozen and you want to know if there is a way to tell whether its frozen in the open or close position without removing the exhaust pipe and physically looking? the answer is no. the reason why is the valve/butterfly piece of sheet metal can spin on the shaft and you wont know it unless you physically look.
start by carefully removing the collector nuts on the manifold. as i've written in my other articles NEVER use an impact gun on these or you greatly risk breaking the brittle manifold. you can use penetrating oil of your choice. i typically skip all that and heat the nuts cherry red with a propane torch prior to removal with a breaker bar. if you feel the nut binding, then reverse your direction and work it back and forth like you would a thread dye or tap. i have great luck with that method 9 times out of ten. if under no circumstance can you remove the nuts without risk of breaking studs or the manifold, then cut the pipe with a sawzall and drill/ remove studs on the work bench. if you've got gaskets installed between the manifold and the head, those should be removed, anyway and bolted on "metal on metal." as described in the "exhaust gasket speech" article found far down on my list of blog articles. if the heat risor valve is frozen open, you can leave it if you desire. if its not frozen, or if its frozen shut, it now must be removed.
now that the manifold is removed/heat risor valve housing is removed use a plasma cutter, small torch, or body saw and remove the valve. if the shaft is frozen solid, leave the shaft. just torch out the sheet metal valve and leave it alone. reassemble it. if the shaf is loose, remove the whole assy, including the shaft. you can run a tap through the side shaft holes and thread a bolt in. usually the tap ends up just pulling the bushing out. you also run the risk of cracking the housing or manifold by try to tap it, as its very brittle. a better option is just run a bolt and nut through each hole with JB weld on it and tighten them down.