Waterless Coolant

You can just have you current radiator checked for flow and blockage and go from there. You can get a high density core put in. Friend has one in his Hemi dart clone. Doesn't run a fan shroud to keep the original as delivered look.

Original 69 m-code 440 darts had fan shrouds. Don't know if the 340 shrouds are the same.

Here is a stock-ish looking aluminum radiator. Various resto parts places sell these. OER is not the only place that sells these. I've seen guys at local swap meet that sell aluminum radiators carry these.

OER Authorized aluminum Radiator