454 Running Hot

Jimmy it is easy to just replace parts replace parts based on age. However I would start with the thermostat and see if it fully opens in boiling water. I think an 84 was a lower thermostat setting (180 degrees). They also sell HD thermostast with a small poppet hole to increase flow. The fact that your system recovers quickly is a good sign. I would buy a HF IR gun and check your thermostat housing and compare it to the temp sensor(sending unit) in the LH head. This will be your temp gauge reading. I found a 20 degree difference on mine. Gauge reading was 20 degrees higher than thermostat housing. Does the MH overheat at idle on a 85 degree day? The next thing I would do is once the engine comes up to temp is to shoot the inlet to the radiator that should be your highest reading then work your way across in a grid pattern to the outlet if you see any cold temp readings this would indicated a plug radiator, look closely where the fan clutch is in the center. If you get uniform decreasing temp readings with no cold spots and a 50 degree drop in temp from inlet to outlet I would conclude your radiator is good. If you haven't already back flushed the radiator with a garden hose at the outlet with the thermostat removed I would do that also. You will have to re-position the fan clutch to take these readings. If your thermostat is the correct one and is opening up all the way, and the radiator is good then I would install an air dam to force air through the radiator and prevent the air from going under or around the radiator. I used thin FG sheets to build mine. Headers and a free flow muffler will also reduce a lot of eng heat. Hope this helps let us know what you find.