Piece identification help

That's a '70-'72 exhaust manifold, and you're asking about the choke thermostat assembly. That '70-'72 exhaust manifold and choke setup has special issues; see here. The original-type '70-'72 choke thermostats can still be found (look on eBay or call up Old Car Parts Northwest) but unless you have a reason why you must use this manifold, you're better off swapping on a new one—uncracked, unwarped, and with the '73-up closed choke pocket setup, much less prone to leaks and hassles; see here. If you do that, you'd want to use a № 1231 electric choke kit.

Either way, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.