Replace; the stock cooling system is bulletproof for many miles but when it goes it sems to go all at once. New rad, thermo, waterpump, and all hoses. If you go to the trouble of pulling it out once you might as well go all the way. The only conditions on this would be if you had replaced all the other parts prior to this issue.
I have babied many a rad enough to get it to work a while longer. If it is that old and original you shoulkd replace it with all the assorted parts.
My theory is that you replace all parts of the system you are working on. Replace as new. That way you no longer need to worry about that system for many miles.