How do you make a 305 engine run cooler in a 86 trans am?

First, start off by making sure your cooling system is in good order. Water pump and radiator.....maybe a good flushing. Drop in a 180 degree thermostat...the ECM will operate ok at that temp, but don't go any lower without a performance chip. One thing most people forget about, ( I did before I knew any better) is the fan clutch. These do wear out. Get a good thermal and rpm sensitive one. My car would slowly overheat on hot days running down the highway. After putting in a new fan clutch that ended. Also, with the lack of an actual grill, the air dam mounted at the bottom of the core support is extremely important. This is what helps direct more air into the radiator. Make sure it's in good shape.....a lot of them are missing from being ripped off by parking blocks. You might want to blow out the radiator and A/C condenser fins. Could be clogged with years of dirt and debris. Is the car overheating or just running hotter than you'd like? If it's overheating and fairly rapidly you could have a blown head gasket.