Hot Cleveland
Well, the first thing you have to do is to put the thermostat back in! The cooling system was designed to have that restriction. If the coolant is going through the radiator too fast it can't cool! A 180 degree stat should be just fine. A 160 degree stat will cause accelerated wear in the engine. That's why most engines after the early 70s came with 195s. The oiling is actually better and lessens the chance for sludge buildup.
Next, are you still running the stock fan? The stock fan and shroud should be plenty good. Wife's 70 Mustang is stock, but even with the high compression motor it has no trouble at all keeping cool. For my 73s, I have the stock flex fan with the thermostatic clutch. No problems at all keeping cool. The key is that you gotta have the shroud! If you live in a very hot region, an auxillary electric fan can be used. You should not use one as your only fan though!
The proper mix of anti-freeze is also necessary to get the proper ammount of heat transfer from the engine. Too much anti-freeze is actually bad! 50/50 is what is recommended by most manufacturers. The coolant also has other additives that are for water pump lube, anti-rust, etc.
How are you sacrificial anodes in your block? There are two zinc rods that are installed through the deck surface that go into the water jacket. When those get eaten away, you'll start geting a rust buildup. When that rust buildup gets thick in the block, your engine will run hot. Once that stuff gets in there it is really hard to get out. The best way is to remove all of the freeze plugs and flush the entire motor out. You can also try to flush it out the old fashioned way. You'd be amazed at how much junk will come out of there!
