Overheating 360 new engine

Uneven exhaust temps are normal, center cyls are always hotter on a small block with stock type cylinder heads. With the cooling issue, you have painted yourself into a corner with your modified cooling system. Some of the above responses are true, some are not. I would never have gone in the direction, or the way that you wanted your engine bay to look, but it's yours, I get it. Now you have found out how incompatible aftermarket parts can be. Your going to spend more money now. You wouldn't want to go with my route, you would be starting over.
Not unusual to blow a freeze plug out either.
Sorry, I can't help you.
Good luck