In addition to the timing recommendations stated, make sure you're getting vacuum and mechanical advance. It almost sounds like the advance is not coming up. You're going to want to start at 12-16 degrees initial and with the light on it, make sure the timing advances as you begin to rev it. If it doesn't jump, you may have a stuck vacuum and/or mechanical advance plate.
Also, you don't say what manifold you have. If stock (or aftermarket spreadbore), I'd sure look at putting the Quadrajet back on it! Those small primaries will give you more velocity and low end torque, than the 500 CFM you're running now. It'll also give you better fuel economy and performance. The Q-jet is hard to beat in my book.
Start with sorting out any/all timing issue first, though.
When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.