I have a 1984 C20 diesel with a J code engine.

I snapped a bolt trying to replace my thermostat. Long story short, after a few botched attempts at extracting the broken bolt I may need to replace the manifold that the wateroutlet/thermostat housing was attached to. The manifold is mounted to the front of the block with four bolts and connects via hoses to the heater core, waterpump, and thermostat/water outlet to the radiator and water jacket.

What is this manifold called?

If you are feeling generous- where might I find a part like this? Salvage?

Thanks, Noah.

the crossover?

Coolant crossover, the single thermostat one is better don't but a dual thermostat if you think its an upgrade.

Thanks. I appreciate it.

Real common for electrolysis to attack those bolts and corrode the crossover.