Like I always say, when doing this mod, the first step should always be to unbolt the fan relays from the passenger side inner fender. Pop the connectors out, and painstakingly remove all the 20 year old die electric grease from all the pins and sockets, using ronsonol lighter fluid (yellow bottle), wire brushes, picks, blow gun, etc. Get them all sparkling clean and spray WD-40 in the sockets and you're good to go. That old grease turns to this roofing tar like substance that KILLS conductivity and causes a huge amp draw...bad for the whole electrical system and it causes the fan to spin slow. The little coil in the fan delay box...the tiny leads fry like a fuse after being exposed to these high currents, so take care of that. Get yourself a 50 watt, .1 ohm fuse, and use that fuse instead of the factory one...just disconnect the leads to the factory fuse and solder the leads on the new resistor. Now when the low fan circuit kicks on, the "low speed' will be alot faster than stock slow speed, but not full blown high speed that'll wear the fan motor out and cause funky imbalance vibrations that resonate through the whole car (if your fan is out of balance at all). This isnt necessary but it made a big difference on mine. I use the stock fan and it works liek it should. It runs 162 degrees all the time, except stop and go traffic where it hits 168, rarely up to 172. I popped the thermostat housing out along with the thermostat, and pulled the lower radiator hose off at the radiator (obviously you have to to replace the radiator)...get a garden hose and flush the whole cooling system out..the crud in the system will coat the aluminum surfaces in the tubes and affect conductivity alot more than you realize. Stick a hose where the thermostat goes on the intake, and flush all that out. Then stick the hose in the lower radiator hose and flush it that way (watch out cause it'll be spraying out of the front of the intake). Flush the other way again, and the other way again. NOW after all this, theres actually a point to all this.
Call the local autozones and find the cheap aluminum radiator for the 87-89 Z-28's and IROC camaros. I spent 108 bucks for mine. I drops right in. Just make sure the rubber pads that support the radiator, below and on top are located right or you'll squish the radiator and can cause little cracks at the fins. Buy a new radiator cap. get it all back together, fill it up with 30% antifreeze and 70% distilled water from the grocery store. The high water percentage s heat transfer. Adding a bottle of watter wetter makes it even better, but I dont need it with the mixture I use. Fire it up with the radiator cap off, let it warm up and wait for the thermostat to open. The water level will drop quick and keep filling it till it tops off. Grab the upper radiator hose and squish it quickly severeal times, then the lower hose, then the upper again, etc...to pulse all air pockets out of the system. But watch out cause it'll pump coolant out of the radiator cap hole and burn you. Keep a close eye on the temperature cause if you have any air pockets, it will overheat quick. But the pulsing of the hoses will take care of that. You'll be good to go.