The stock crank pulley is usually 7" to 7 1/4". Fan pulleys vary depending on setup... mostly "with" or "without" AC. The "with AC" setup has a smaller fan pulley that overdrives the fan and water pump for better cooling. Bouchillon covers pulleys well (link attached).

Back to the "rule of thumb". You are running 200 on the highway. Warmer than your stat temperature assuming your gauge is accurate but not really overheating. 220 or 230 is getting a little warm.

I think your system could be minimally OK with addition of a shroud to help low speed cooling. The fan without shroud moves air but not so much through the radiator. These cars need a shroud for low speed cooling performance. This is a first step.

If there is question, verify the gauge. I like to use a low cost mechanical gauge from the parts store installed temporarily to measure coolant temp directly. Sometimes you can tell by how your current gauge acts from cold start. Start cold and drive moderately on the highway and watch it. Does temp rise gradually for a while, then level off for a while then start climbing again? If it levels off around your stat temperature (180) then climbs after that suggests gauge is close and stat is working.

It would not hurt to research pulley ratios. At least some overdrive of fan and water pump helps cooling.

And finally, you may need more radiator. FWIW I run a 26" "muscle car" aluminum radiator from Mancini with their matching shroud on a warm 496. This is a high capacity downflow radiator. Cooling is excellent (with AC). It stays right at 180 stat temperature rolling - even racing - and a little warmer with extended stop.

www.bouchillonperformance.com