Not your normal Mopar cooling issue

Mopar Vince said
Yes, restrictive exhaust?
Yes, lean?
195-ish ok then?

Could be lean. You'd have to read plugs or plumb in a wideband o2 sensor. The 273 manifolds are definitely a restriction. As long as the engine doesn't climb to 230°+ you should be fine. It apparently climbs and stabilizes.