I would remove the radiator and find a better one that was designed for a Gbody in my Regal I installed a Champion 3 row aluminum radiator and it fit perfectly in my stock shroud, later I will be installing a SBC in there and I already have a dual fan Interepid set waiting for the swap but you could run your new radiator with a stock shroud and fan first and will probably resolve your cooling issue.
Below is a picture of my project Regal with the Champion radiator and stock set up and you can see where the blades should be in relationship to the shroud.
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