You can either do a search on "manual fan switch" to see how to make what I'm making or you can buy a fan switch from Pep Boys that will automatically turn on the fan for you at a desired temperature. Do not buy a $500 tuning device just to turn your fan on sooner. You will be wasting your money on a bone stock stang. People will tell you to anyways just to try and "sell" the Tweecer or whatever they use but its not worth it. If you must, just get a chip to do the same thing. Much cheaper. Just remember though, that if you do get the car to run cooler and the pinging goes away, unless you are currently overheating, this is only a bandaid fix. If your car is not currently overheating and cooling it down fixes the pinging, then the cause of the pinging still exists which means you could still have a bad sensor, fuel pump, ect, ect somewhere.
The thermostat by itself is not going to do much. As long as your fans are kicking on at 210 or so, the car will rarely see 160 or 180. So you are pretty much keeping the tstat open all the time during normal driving conditions. You need the airflow as well to get it even close to that low. Even then, you wont get it to 160 and shouldnt get it to 160. You should be running a 180 tstat at the lowest. Some people will even tell you that 180 is too low.
And I know you still think that retarding timing is going to cut HP but it wont if the extra timing is killing your performance to begin with. You can run 30 degrees of timing but the optimal setting for your car may be 10 degrees. That may just be where your car wants to run. Anything more and it may ping and create LESS horsepower. You are only going to get HP where the car will run properly. Sometimes you have to decrease timing in order to pick up HP. Gaining HP isnt really about having the most of this, the biggest that and the highest flowing this. Its about having everything optimized for what is best for what you currently have. On a stock car, you dont need much timing.