Where to start?

With distributor locked out and you have only 24 degrees of timing you may be getting spark jumping between terminals in the cap when you start to rev it up, especially if the rotor is not phased correctly. Bump up the timing like noted above and see if that helps. I had a similar issue when I broke a new cam in, just set dizzy to where it would run to break it in and forgot to set it with a light on first test drive, would start missing at 5k, bumped it to 34 total and no more missing.