Hei conversion troubleshooting

Sorry Andy way to many names. It should be ported for the vacuum advance. That can possibly be the issue. I do not remember the amount of vac advance on that one. Just say it is marked 10 on the arm that is 20 degrees on the crank. OK for numbers sake you set it at TDC with a light then hook up manifold vacuum that is 20 right from the start then you start adding the mechanical in as you add rpms, it get really high fast. Is it pinging right before the stumble?