Radiator Interchange 1974 Dart /6

Your 74 should have a 26" opening in the core support. So you have the option of getting v8 heavy duty radiators for A-bodies, anything else will likely require some level of modification to fit.

I had a quite stoutly built \6 in my 68 Barracuda for 4 years and never had an over heating problem with the stock \6 radiator. If there is nothing wrong with the radiator you have I wouldn't worry about changing it until after you get your mods done.