Battling overheating new 360 build

185 at the sender, with the guage centered, would be about right for a 180 stat.
There are exhaust cross-over ports on the manifold that'll be way hotter than the coolant temps.

I humbly suggest that you install a mechanical guage to be sure.
With your rad dumping all that heat, I'm getting the feeling all has been normal since the new un-plugged rad.