I'd pull them all just in case there is something different front to back.
I caught the check on the temp gauge so feel your gauge is not lying to you. I just have to wonder if your t'stats are being pushed open by the pump pressure; this is something that you cannot test on a stove. They DO have to have a certain spring pressure to keep close in the presence of the water pump's pressure. Only replacing with a good one will determine that. (I can't tell you how to test the spring pressure.)
The fact that you see water flow to the top of the rad at a temp on the meat thermo that is well below the proper t'stat temps says that the t'stat is somehow opening.... or there is some way that the coolant is bypassing the t'stat. Are the t'stats sitting very snugly in the recess in the housing? Have you looked at both the manifold AND the t'stat housing to be sure that there are not recesses in both that can allow flow around the outer edges of the t'stat?
What brands are the t'stats please?
Any thing odd in the head gaskets? Is this a Magnum 360? Just wondering if the head gaskets could have gotten flipped front to back and the coolant is not following the right flow pattern.