no way in hell would I put a DP carb on that. Nor would I bother wasting money on a quadrajet. Your current carb will work perfectly- if it is cleaned up and tuned properly.
BTW, why do you want your secondaries to open sooner? That would be the first question I would want to answer. Next, if you need to change your pump cam, do it. You can also change your squirters if that is the problem. And as suggested I would convert to 4150 immediately.
You have an untuned carb, and any untuned carb is NOT going to perform well. Changing to a different untuned carb still will not fix your problem.