[Car Nut]

I see two issues.

The timing marks on many aftermarket dampers aren't indexed correctly to the timing tab on the passenger side of the engine (when using a driver side water inlet for the water pump). They were designed for a tab on the drivers side. Not sure if yours is this way. You can check this by putting it on TDC (between the compression and power stroke) and checking the mark.

I have the same distributor. I run a base timing of 18 degrees with a total of 36 degrees. The vacuum advance adds another 20 which makes it pop and snort over 2500 rpm in cruise. That is just way too much timing for my motor. I run it without the vacuum advance and it performs just fine. Could it be that someone put a stop on the vacuum advance and it fell off?