A couple things to think about.
the V6 core from a car or truck? a car radiator is lighter duty than a truck radiator.
is it a side flow radiator or vert. flow? side flow radiators will be a bit more efficient than others.
and the obvious,, is it clean and in good working order?
Auto trans or manual? if its auto, DONT use the built in trans cooler tube, get an external trans cooler. (manual trans uses no cooler)
I have built a V8 vega and used a side flow V6 radiator from a pick-up, installed 2 electric fans on it and a high flow water pump, my car would run a bit hot in town sitting at lights, (225'-240) but when moving I never had a problem (220')..
anything 250'+ is TOO hot, but there are things you can do.
fan shrouds, ducting, and sometimes you can remove the thermostat, punch out the center part and replace it, that way you still have a bit of restriction needed for cooling and unless you live in a cold climate you wont have winter heater problems.