The instant invention is directed to a process wherein a heavy oil feedstock upgrader alters its mode of operation of its full conversion hydroprocessing unit to create a custom tailored synthetic crude feedstock based upon data communicated from a target refinery and data communicated from the heavy oil feedstock upgrader. The data from the target refinery is data that represents refining process data and linear program modeling along with analysis by a refining planner to calculate the optimum “synthetic trim crude” that will optimize the effective use of the target refinery's capacity and equipment.