I just hit 494k miles yesterday. My dad and grandfather built the 361 currently in it and put it in around 100k. At around 450k miles I removed the oil pan and the timing cover to reseal the lower end. While I had it off I plastiguaged the berings and they all looked good. I replaced the oil pump, fuel pump, sparkplug wires, distributor cap and rotor, valve cover gasket, t-stat and radiator lines. I also rebuilt the carb.
What all should I start looking at when I hit 500k?