Looking for a little advice on the timing numbers I just pulled from my 73’ Duster (backfire issue)

Thanks again! Looks like 5 degrees made all the difference. One last question I had is that with the vacuum advance connected and the car in Park the idle is right in the 860-900 range. Is that a little too high? Sounds good and runs well. Especially when in drive and my foot on the brake.
Drop the idle to around 750 rpm. Since someone went through the trouble of adding a 4bbl and manifold, they might have changed the distributor too. See if you can find a tag or a number stamped on the outside of the dist. housing.