I tested my thermostat today.

Here's a short video showing the results: 170 degree Motorad Thermostat operation - YouTube

I couldn't find any other videos showing how it should open at a given temperature, so I'm not totally sure what to conclude from the test but i can at least say it opens. It cracks open later (~178 degrees) than it's rated (170 degrees) then doesnt really open wide until nearly 190 and fully open at 195+.

Like i said, idk if that's completely normal operation, but it does open and shut.

If we can agree that the thermostat is working well enough, the only things left to do is make sure the lower hose isn't collapsing (it's already more bent than normal because of a body lift) and take it to a shop for a chemical flush. The coolant passages on the head that wasn't replaced, the block, the radiator, and everything i could see when i had the heads and water pump off looked very clean. But the junkyard head that I put in had coolant passages that looked like they had a lot of crap in them... I really shouldve had that cleaned out when it was at the machine shop.