I've cooked my 88 300 several times with no problems after it cooled down.
I've had my 85 300 up to at least 235 because of low coolant. I think the factory gauge was just past the L at that point. On the 88 with a undersized radiator I would often run it past the L up to the far line. I think the factory gauge works perfectly. You must keep in mind factory electric fans were often not programmed to turn on until about 238 degrees. I like to keep my engines warm, ideally 210. I get worried above 230 but that doesn't stop me from driving until I get another symptom.
I've had my 85 300 up to at least 235 because of low coolant. I think the factory gauge was just past the L at that point. On the 88 with a undersized radiator I would often run it past the L up to the far line. I think the factory gauge works perfectly. You must keep in mind factory electric fans were often not programmed to turn on until about 238 degrees. I like to keep my engines warm, ideally 210. I get worried above 230 but that doesn't stop me from driving until I get another symptom.