Overheating?

[hawkgoalie31]

I have a 1974 duster with a 318 that used to have 245s in the rear and I switched them to 355s witha 3 speed tranny. So when I drive the freeway naturally the engine revs high. I live in so cal so it can get pretty hot and my car runs up to about 210. Whats a temputure that I need to be worried about my car overheating at.

Thanks