Re: new crown molding meets existing cabinet crown molding
It's a bit of a skill to cope one molding into a different one, but eminently do-able. You first should procure a set of scribes, but a compass like you used in 7th grade geometry will do. Hold a short length of the new crown up so that it contacts the cabinet crown. Set the scribes to the distance of the largest part of the gap. Hold the scribes in an horizontal plane, and trace the cursor (pointy end) across the cabinet molding while the pencil end transfers its profile to the new crown. Visualize how the coping saw needs to cut straight back into the new wood to allow it to conform to the cabinet crown. Cut this line. Try the fit and correct the cut by paring away more material as required.
Remove not the ancient landmark, which your fathers have set.