Have to look at each piece of the puzzle separately. Fresh engine was it hot tanked and cooling passages cleaned and then recleaned and visually inspected. The Water pump and housing are they mated and just what water pump are you using. The rad, is it new has it been recored, what rad is it and how many cores. Thermostate I run 160 but other temps are fine when your system is working perfectly. Is this motor completely stock with no adjustable rockers and everything like cam timing and distributor timing set correctly. All thing I have mentioned can affect how hot the motor runs. There are a lot more things that affect motor heat. Look at one part of the cooling system at a time. Start with the RAD since you say it is cool on the top and hot on the bottom.