Slight miss in my 69 Z28

[sixt9rsx33]

Did a few tests today. And I found this to be odd. Had the idle at 900, vacuum line plugged, dial back timing light hooked up, I was only able to get 4* BTDC with the dial on the timing light set at zero. So I was unable to match up the line on the balancer with the 0 on the timing tab. I don't ever recall having this issue with the car. I went ahead and advanced the timing so I could get 4* on the timing light dial with the balancer zeroed out on the timing tab. Took the car for a drive and it spark knocked so obviously too far advanced. I set it back to where it was.
I had 33* total advance at 3000 rpm with no misses or anything weird. The engine purred at 3000 rpm. I also checked the total advance at 2800 and it again was 33*. I did not walk it down to see when the total advance came in.
When I had the gun on the tab at 900 rpm the engine would miss and the timing light would go dark instantly and then come back on. When the light came back on you could barely see that the timing mark was at like 6* or 7* and then come back up to 4* once it stabilized a little. After the 3000 rpm total timing test I set the curb idle back to 900 and the car idled terribly. The tack needle was bouncing all over the place. The other odd observation that I am noticing that very seldom happened in the past is that the car is dieseling when I turn the car off. I never had this issue before. Now about every third time or so when I turn the car off it diesels. This has got to be ignition issue but I am at a loss. I have not changed the points condenser, plug wires yet. I tested the plug wires and they seemed to be ok. I had a condenser go bad a few years ago but the symptoms where different. I guess I better change the points just to cross that off the list? Any suggestions are appreciated.

Lawrence