396 timing

[GMC69]

I decided today that I should check the timing on the new truck. What I have noticed driving it, is when on the hwy at wot there is a very slight ping, first clue. Also once warmed up, and I am idling downa street and try to accelerate, there is a hesitation/stumble. Also sometimes when starting it. It starts to crank but almost stops then fires right up light really high compression.

The motor is a 396, headers, edlebrock performer intake and a holley street avenger 770cfm carb.

I drove it to get to operating temp, then threw the timing light on it. Rpm is around 700-750 and timing is sitting at about 20 degrees advance.

I am not sure what kind of work was done to the internals, all I know is it came out of a chevelle cause he put a 502 in the chevelle.

I was going to drop the timing to about 16-18 but maybe that is still a bit high.

Any thoughts on where I should be with it?
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