Slant six Holley 2280 stalls when stopping

More timing, not less, should help dieseling. The dieseling is caused by high idle speeds. Get the speed down, D stops. More timing usually increases idle speed. But at the same time it makes the engine more efficient [ speed went up using same amount of A/F ]. Once the speed is up from more timing, try re-adjusting idle speed screw & mixture screws for lower idle speed.