Hi Denny,
It is a mistake to replace the aluminum radiator in my opinion but please understand I live in Dallas (which some have called the waiting room for hell, weather-wise). We get summer apx 8 months a year so maximum heat transfer is of paramount importance, and the old copper/brass radiator falls to second place behind the aluminum one. Since your engine (a 261) wasn't available when your truck was made and since you have an alternator rather than a generator, you've already stepped outside the parameters of "restoration." If you have a 3 row aluminum radiator I'd leave it.
