timing advance (to much)

Total advance of 50 with the vacuum advance disconnected is WAY too much. I would go no more than a total advance of 36 (no vacuum advance) and then plug your vacuum advance back in and you shouldn't have any problem. If you get pinging then set it up with a total advance of 34. If it's still pinging then cap off the vacuum port.

My small block is really too radical for 92 octane and I have to have at least 96 octane to stop the pinging. If your pinging at a total of 34 degrees total mechanical advance you have two choices, back off even more, or buy some 118 octane racing fuel and mix it with high octane pump fuel until it stops pinging.