From what I have seen the stock 383 radiator is physically the same size the inlet and outlet is larger in diameter.
I am sure the fins per inch and the construction of the tubes is different, not to mention the water pump, pulleys, etc.
I have a stock HP/AC radiator and a stock standard cooling rad. The tubes are the same except the HP/AC rad the tubes are (just numbers for example) 1/2" long by 3/16" wide vs 1/2" long by 1/8" wide.
All I'm going to say about the subject. If you think I'm full of **** so be it. I know what has worked and what hasen't in my life experience.