What is a Magnum 250? Do you mean the Magnum 294S which has a duration of 250 @ 050? If that is the cam you are talking about then it should be fine for a 512 inch street engine. It might not be big enough to make 650 hp but it will pull hard in a pump gas 512, especially with the 1.60 rocker arms. You can go larger with the cam but you'll start to give up street manners so then it just depends on how much you're willing to live with on the street.