Cooling system Q's

[66jax]

Alright guys, I am new to the truck building game but am learning as I go. I have a '66 c10 with a 305 V8. I have installed a painless wiring kit and am about to purchase a champion 2 row aluminum radiator with 16" fan. I am going to replace the water pump as well. My question is thermostats, how do I know which one to buy? Do not know if this should be common sense. Had overheating issues at they Turkey Rod run with belt slipping and now it heats up very quickly in traffic, before the rod run never had an issue. Any help will be greatly appreciated.
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