After A/C Add On Engine Overheats Really Bad

I borrowed a picture that would look exactly like my Dart for my avatar until I got mine finished. Now that it is finished I will be changing my avatar when I get some pics put up! The a/c belt runs around the compressor, a separate crank pulley, and a single side pulley. It doesn't involve the water pump pulley. However today I messed with the timing some more, tapped the key and it started right off, checked the timing, ran it without the radiator cap and checked for flow, which there is, maybe if there was some air in there, maybe it got out, then put the cap back on. I let it idle with the a/c on for a loong time, and the temp needle sat in the middle of the gauge. I also sat with it in drive for a long time and the temp didn't move. This was in my storage building with no air movement. I shut it off several times and it restarted each time. So I'll see how it reacts when I drive it again. Thanks for all the suggestions...I'm sure I won't be through with it!

So where do you find Milodon thermostats?