210 is pretty normal. That said, have you had the radiator checked out? When the engine was "rebuilt" was it sent to a shop to have it hot tanked and all the coolant passages cleaned?
Answering a question with a question may not be considered proper.
Regardless, I think questioning the radiators condition is the best response here.
With 3/4 of scale on the stock gauge, I would have questioned the radiator before the rebuild.
