1965 270 dart 225 ci slant six radiator

No, the '64 radiator will not bolt into the '65 car. Direct interchange is '65-'66 A-body with slant-6, if you want an original-type radiator. '67-'76 A-body slant-6 radiators can also be made to fit without too much work ('70-up needs different lower hose). If you want a new radiator you won't have to think about again for many years, and have the money for it, do like this.