if the system is clean and you don't have too high a pressure cap, 'these old radiators' are as good as new ones - you could take the rad to a shop and have it checked, but if it hasn't been abused it'll do fine, more likely to have water pump or fan belt problems
I've driven hundred + mile round trips numerous times in my 58, did in the 57 panel I had as well .... I took a 55 International panel I had right across the country 3 times, never any cooling system problems on the road, summer or winter
OTOH, a steady 65 with a 6 and the stock gearing is stressing the engine pretty good, the rad would be the least of yer problems
Bill
